GWH 425 PN
INDOOR MODEL
Flow Modulated with Standing pilot
Suitable for heating potable water only - Not approved for space heating purposes
(Intended for variable flow applications with steady cold water inlet temperatures)
GWH-425-PN-N
GWH-425-PN-L
Warning: If the information in this manual is not
followed exactly, a fire or explosion may result
causing property damage, personal injury or death.
Do not store or use gasoline or other flammable
vapor and liquids in the vicinity of this or any other
appliance.
What to do if you smell gas
Close gas valve. Open windows.
Do not try to light any appliance
Do not touch any electrical switch; do not use any
phone in your building.
Immediately call your gas supplier from a neighbor’s
phone. Follow the gas supplier’s instructions.
Improper installation, adjustment, alteration,
service or maintenance can cause injury or
property damage. Refer to this manual. For
assistance or additional information consult a
qualified installer, service agency or the gas
supplier.
If you cannot reach your gas supplier, call the fire
department.
Installation and service must be performed by a
qualified installer, service agency or the gas supplier.
In the Commonwealth of Massachusetts this
product must be installed by a licensed plumber or
gas fitter.
Upon completion of the installation, these
instructions should be handed to the user of the
appliance for future reference.
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Appliance details
2
Appliance details
Dimensions
2.1 GWH 425 PN specifications
(Technical data)
GWH 425 PN:
Depth (in): 8.66” (220 mm)
Width (in): 18.11” (460 mm)
Height (in): 25.79” (655 mm)
Weight: 35 pounds (16 kg).
Approved in US/Canada
Capacity
GWH 425 PN: 4.3 GPM
Maximum output
Gas types
GWH 425 PN: 91 525 Btu/hr
Natural Gas.
LP Gas
Maximum input
GWH 425 PN: 117 000 Btu/hr
Safety devices
Efficiency in %
Flame failure device (ionization flame rod sensor)
Pressure relief valve (supplied with heater)
Over heat prevention (temperature limiter).
Recovery efficiency 78%
Min. Output
GWH 425 PN: 23 906 Btu/hr
Water resistant
Gas Requirement
IP X4.
Gas connection (inches) - ¾” NPT
Inlet gas pressure under maximum operation*
Propane: 10.5” - 14” water column
Natural Gas: 5.7” - 14” water column.
* To measure Gas Pressure, see Measuring Gas
Pressure, chapter 3.8.
Venting
Natural Draft
Vent diameter (inches) - 5”
Minimum height (feet) - 6’ with no elbows
Vertical termination
Sidewall termination only with AQ4 power vent kit.
Water
Hot water connection (inches) - ½” NPT
Cold water connection (inches) - ½” NPT
Water valve material: Polymer (PPS) (Polypropylene
Sulfid)
Minimum water flow: 0.5 gallon/minute (1.9 l/m)
Minimum recommended water pressure: 30 PSI
(2.07 bar)
Connections:
– Bottom of heater
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Appliance details
2.2 Unpacking the GWH 425 PN heater
2.3 General rules to follow for safe
operation
This heater is packed securely.
1. You should follow these instructions when you install
your heater. In the United States: The installation must
conform with local codes or, in the absence of local
codes, the National Fuel Gas Code ANSI Z223.1/
NFPA 54.
Before installing the unit, be certain you have the
correct heater for your type of Gas - Propane or
Natural Gas. Identification labels are found on the
shipping box, and on the rating plate which is located on
the right side panel of the cover.
In Canada: The Installation should conform with CGA
B149.(1,2) INSTALLATION CODES and /or local
installation codes.
2. Carefully plan where you install the heater. Proper
clearances must be followed.
3. The appliance must be isolated from the gas supply
piping system by closing its individual manual gas
shutoff valve (not supplied with heater) during any
pressure testing at pressures in excess of ½ Psig (3.5
kPa).
The appliance and its gas connection must be leak
tested before placing the appliance in operation.
4. Keep water heater area clear and free from
combustibles and flammable liquids. Do not locate the
heater over any material which might burn.
Fig. 2 Rating plate
5. Correct gas pressure is critical for the optimum
operation of this heater. Gas piping must be sized to
provide the required pressure at the maximum output of
the heater, while all the other gas appliances are in
operation. Check with your local gas supplier, and see
the chapter 3.7 and 3.8 to verify proper gas line sizing.
A
B
Serial number
Type of gas
The box includes:
Pressure relief valve
Mounting screws
6. Should overheating occur or the gas supply fail to
shut off, turn off the gas supply at the manual gas shut
off valve, on the gas line. Note: manual gas shutoff valve
is not supplied with the heater.
Product registration card
Installation manual
Incandescent particle tray.
7. Do not use this appliance if any part has been
Do not lose this manual, there is a charge for a
replacement.
Please complete and return the enclosed product
registration card.
underwater. Immediately call
a
qualified service
technician to inspect the appliance and to replace any
part of the control system and any gas control which
has been underwater.
The GWH 425 PN is not approved or designed for:
Manufactured (mobile) homes, RV's or boats
BOSCH is constantly improving its
products, therefore specifications are
subject to change without prior notice.
i
Heating or other recirculating/pumping applications*
Solar/preheat backup or high temperature booster
use
Installation in a bathroom.
* This includes domestic hot water circulator pump loop
systems that may be installed in home hot water system
prior to installing this unit. An approved recirculation
design can be found in chapter 3.10. Contact BBTNA
if further instruction is needed.
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Appliance details
2.4 Dimensions and installation clearances
Fig. 3 Dimensions in Inches and (mm)
4
5
Heat exchanger
Burner
Dimensions inches
(mm)
10
11
20
26
36
37
38
39
40
49
102
Temperature control
Water valve
Gas connection
Output control
GWH 425 PN
16.73” (425)
25.75” (655)
13.15” (334)
5.11” (130)
21.25” (540)
2.55” (65)
Front cover
A
B
C
D
E
F
Hole for fixing to wall
Exhaust pipe to wall
Draught diverter with flue gas monitor
Gas valve
Observation window
Piezo
G
H
1.18” (30)
3/4”
Table 1 Dimensions in inches (mm)
Model GWH 425
TOP (A)
12 inches (306 mm)
4 inches (100 mm)
0 inches
FRONT (B)
BACK
SIDES
4 inches (100 mm)
12 inches (306 mm)
BOTTOM (C)
Fig. 4 Minimum clearances
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Installation instructions
3
Installation instructions
3.1 Introduction
Warning: The heater must be isolated
from the gas supply piping system
during any pressure testing of that
system at test pressures equal to or
more than 0.5 psig.
Please follow these instructions. Failure to follow
instructions may result in:
B Damage or injury.
B Improper operation.
B Loss of warranty.
Warning: Place the heater in a location
where water leaks will do NO DAMAGE
to adjacent areas.
If you are unable to perform the tasks required to install
this heater properly, please contact a locally licensed
plumber or gas technician.
Please contact Bosch Water Heating with any
questions.
3.3 Heater placement and clearances
The GWH 425 PN is design certified for installation on
a combustible wall (see 3.4 Mounting installation)
provided the wall is not covered with carpet or other
fabric material. For installations in an alcove or closet,
maintain the minimum clearances to combustible and
non-combustible materials listed below. See also Fig. 4.
3.2 Proper location for installing your
heater
Carefully select the location of the water heater. For
your safety and for proper heater operation, you must
provide combustion air to the heater and a proper
exhaust vent system.
A. Top 12 inches (306 mm)
B. Front 4 inches (100 mm)
C. Back 0 inches
Follow the guidelines below:
B 1. Locate the heater where venting, gas and
D. Sides 4 inches (100 mm)
E. Bottom 12 inches (306 mm)
plumbing connections are feasible and convenient.
B 2. The hot water lines should be kept short to save
energy. Centrally locating the water heater is best. It
is always best to have hot water lines insulated.
Warning: The water in this water
heater is cold and always remains cold
except for the times that hot water is
being used. DO NOT INSTALL IN AN
AREA WHERE IT COULD FREEZE.
Drain the heater entirely if freezing
temperatures are anticipated in area
where heater is installed. See chapter
4.5 for draining instructions.
To prevent freeze damage from residual
water in the heater, introduce short
bursts of compressed air (20-40psi)
through these connections to remove
the residual water in the horizontal
pipes and water valve.
Warning:
Flammable
materials,
gasoline, pressurized containers, or any
other items or articles that are potential
fire hazards must NOT be placed on or
adjacent to the heater. The appliance
area must be kept free of all
combustible materials, gasoline and
other flammable vapors and liquids.
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Installation instructions
B Hang heater on two L shaped hooks. (See Fig. 8).
3.4 Mounting Heater
Warning: before starting installation:
B check that there are no loose parts
inside the appliance
B ensure that gas pipe, gas valve, and
burner have no damage and are
properly fitted.
B Read chapter 2.2 to verify proper gas
type and to check all parts are included
in box.
Front cover should be removed in order to
inspect components visually (see
instructions below).
i
Fig. 6 Remove front cover
Remove cover and inspect.
B Remove the temperature control.
B Unscrew the cover fixing screws, see Fig. 6.
B Remove the outer case by sliding it forwards and
then lifting upwards.
B Ensure that the flue terminal is clear.
B After inspection, replace front cover and tighten
screws.
Install incandescent particle tray.
B Install incandenscent particle tray using screws
provided as shown in Fig. 5.
Fig. 7 Support board
Screws
Incandescent particle tray
Fig. 5 Incandescent particle tray illustration
Mounting heater.
The GWH 425 PN is design certified for mounting on a
wall.
Warning:
B Do not install this appliance on a
carpeted wall.
The heater must be mounted on a wall using
appropriate anchoring materials. If wall is a stud wall
sheathed with plasterboard, it is recommended that
support board(s), either 1x4’s or 1/2" (minimum)
plywood first be attached across a pair of studs and
then the heater should be attached to the support
boards, see Fig. 7.
Fig. 8 Secure heater to wall
B Secure the two included L shaped hooks to wall
studs or support board 13 1/4” apart. (See Fig. 7).
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Installation instructions
Fuel Gas Code for complete information. In buildings of
tight construction all air should be taken from outside.
3.5 Combustion air requirements
The BOSCH PRO water heater holds cold water in its
copper heat exchanger and water valve when not in use.
Because of this, any cold air that comes down through
the unit's vent pipe is capable of freezing these
components. This Installation Manual specifies the
minimum vertical vent pipe and the amount of
combustion air required for this unit. When all
requirements are followed, the unit will operate properly
and safely. However, there may still be a risk of freezing
due to negative draft if all the combustion appliances in
the building or structure are not being supplied with a
sufficient amount of make-up air. A wood stove or
furnace can pull outside air down through the BOSCH
PRO vent pipe and across the heat exchanger tubing. If
the air is cold enough, the heat exchanger is at risk of
freezing and bursting. Supplying more combustion air
for all combustion appliances is the solution. Follow the
instruction on venting and checking the adequacy of
make up air. A HVAC specialist should be consulted on
how to provide more combustion air if necessary.
Observe the following instructions concerning
combustion air.
Appliances located in unconfined spaces:
a) An unconfined space is one whose volume is greater
than 50 cubic feet per 1000 Btu per hour of the
combined rating of all appliances installed in the space.
That would be 5850 cubic feet for the BOSCH PRO
GWH 425 PN alone.
b) Installations in structures that have been tightly
constructed (air infiltration rate of 0.40 ACH or less)
must be provided for combustion air per the National
Fuel Gas Code. Consult a HVAC specialist if your air
infiltration rate is questionable.
Appliances located in confined spaces:
The confined space must be provided with two
permanent openings, one commencing within 12
inches of the top and one commencing within 12 inches
of the bottom of the enclosure. Each opening must have
a minimum free area of one square inch per:
1000 Btu/hr if all air is taken from inside the building.
2000 Btu/hr if all air is taken from the outside by
horizontal ducts.
4000 Btu/hr if all air is taken from the outside by
direct openings or vertical ducts.
Or the confined space must be provided with one
permanent opening or duct that is within 12 inches of
the ceiling of the enclosure. This opening must have a
minimum free area of one square inch per:
3000 Btu/hr if all air is taken from the outside by a
direct opening or vertical duct.
Louvers, grills and screens have a blocking effect. If the
effective free area is not known, increase the sizes of
your openings by 400% if your louvers are wood and by
135% if your louvers are metal. Refer to the National
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Installation instructions
B All gas vent sections must be secured to each other
3.6 Venting
with sheet metal screws and be properly supported.
Danger: Do not reduce the vent pipe
Horizontal runs:
size. Do not put an elbow directly on top
of heater. Failure to follow venting
requirements may cause dangerous
exhaust gases to enter living space.
Any gas vent section that is greater than 45 degrees
from the vertical is considered horizontal. Horizontal
sections must slope upwards at least ¼ inch for every
foot of its horizontal length and be properly supported.
Keep the horizontal section short and avoid too many
elbows. The maximum horizontal run allowed is half of
the total vertical vent height; horizontal vent connectors
and elbows are not to be considered in the total gas
vent height.
B Minimum vent pipe diameter: 5 inches
B Minimum vertical vent height: 6 feet, with no elbows
B Establish 12 inch rise before any elbow
The heater must be vented to the outside following all
local ordinances and specifications for installing a gas
appliance vent or chimney. The heater must be located
as close as practicable to a vertically rising chimney or
vent that has a listed vent cap at its termination point.
The venting system must be designed and constructed
so as to develop a positive flow adequate to remove flue
gasses to the outdoors. Consult the National Fuel Gas
Code if the vent will have elbows or share venting with
another natural draft appliance.
Vent termination:
The gas vent constructed of double wall Type B gas
vent must terminate above the roof surface with a listed
vent cap at a height that's in accordance with Fig. 11
and table 2, provided it is at least 8 feet (2.4 m) from a
vertical wall or similar obstruction. All other gas vents
that are not able to terminate within the minimum
specified height allowed must terminate not less than 2
feet (0.6 m) above the highest point where it's passed
through the roof and at least 2 feet (0.6 m) higher than
any vertical wall or similar obstruction within 10 feet (3.1
m).
Warning: Do not combination vent with
a mechanically vented appliance.
LISTED VENT CAP
3.6.1 Horizontal venting
Warning: Horizontally venting to a
vertically constructed vent stack along
an outside wall of a building is not
permissible.
MINIMUM 6
FEET (1.8M)
Warning: Horizontally venting to a
sidewall vent terminator (without power
vent) is not permissible
LISTED GAS VENT
A power vent, with a proof-of-draft safety interlock
device, is required and is available for sidewall venting.
Contact your dealer. In the Commonwealth of
Massachusetts power vented applications must utilize
proof-of-draft safety interlock device.
ESTABLISH A ONE
FOOT RISE BEFORE
ANY ELBOWS
3.6.2 Vertical venting
B
A 5 inch diameter gas vent constructed of double
wall Type B gas vent is recommended. A 6 inch vent
is required in elevations greater than 2000 feet, see
Fig. 10. Under no circumstances should the vent
pipe be reduced in size.
Fig. 9 Flat roof
5” X 6” ADAPTOR
USED ON HIGH
ALTITUDE
B An approved gas vent connector must be attached
to the top of the water heater and rise vertically at
least 12" before entering into an approved gas vent
connector elbow.
B
The minimum vertical gas vent height allowed is 6
feet; horizontal vent connectors and elbows are not
to be considered in the total gas vent height.
Fig. 10 Vent Adaptor for High Altitude Installations
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Installation instructions
Masonry chimney
LOWESTDISCHARGE
OPENING
LISTED VENT CAP
Masonry chimneys shall be built and installed in
accordance with NFPS 211 or local codes. A minimum
5" diameter gas vent pipe (metal double wall Type B),
or an approved clay flue liner or a listed chimney lining
system must be used when venting into a naturally
drafting, internal masonry chimney. 6 inch is required in
elevations greater than 2000 feet, see Fig. 10. Local
codes may require the use of both gas vent and an
approved lining system when venting into a masonry
chimney. The Commonwealth of Massachusetts
requires the use of a listed liner. Lining systems include
approved clay flue lining, a listed chimney lining system
or other approved material that will resist corrosion,
erosion, softening, or cracking from exhaust flue gases
at temperatures up to 1800 degrees F. The lining
system must be listed for use with naturally drafting,
draft hood equipped gas appliances. Follow local
codes and refer to NFGC 54 and NFPA 58.
H (minimum) height
from roof to lowest
discharge opening
X
12
ROOF
PITCH IS
X/12
MINIMUM 6
FEET (1.8M)
LISTED GAS VENT
ESTABLISH A ONE
FOOT RISE BEFORE
ANY ELBOWS
Existing interior masonry chimney
Fig. 11 Pitch roof
The metal gas vent pipe should be permanently
mounted inside the masonry chimney. Double wall Type
B gas vent is recommended. The masonry chimney may
have to be tile or metal lined before the insertion of the
gas vent pipe; check local codes for clarification. The
lining material must be listed for use only with naturally
drafting, draft hood equipped gas appliances. Follow
manufactures instructions for installation of listed lining
material. You may not vent any other fuel burning
appliances into any free space remaining in the
chimney. The minimum vertical gas vent length within
the masonry chimney should be no less than 6 ft (1.8
m); the vent terminator should extend at least 3 feet (0.9
m) above where the chimney meets the roofline and at
least 2 feet (0.6 m) higher than any vertical wall or
similar obstruction within 10 feet (3.1 m). The top of the
gas vent should have an approved vent terminator. See
Fig. 12.
GAS VENT TERMINATIONS FOR LISTED VENT CAPS
Roof pitch
H (minimum) feet
meters
0.30
0.38
0.46
0.61
0.76
0.99
1.22
1.52
1.83
2.13
2.27
2.44
Flat to 6/12
1.0
1.25
1.5
2.0
2.5
3.25
4.0
5.0
6.0
7.0
7.5
8.0
6/12 to 7/12
Over 7/12 to 8/12
Over 8/12 to 9/12
Over 9/12 to 10/12
Over 10/12 to 11/12
Over 11/12 to 12/12
Over 12/12 to 14/12
Over 14/12 to 16/12
Over 16/12 to 18/12
Over 18/12 to 20/12
Over 20/12 to 21/12
Table 2
LISTED
VENT CAP
GAS
VENT
VENT
CONNECTOR
Establish a
one foot
rise before
any elbows
Fig. 12 Masonry chimney
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Installation instructions
B Attach the appliance regulator to the inlet gas pipe.
3.7 Gas piping & connections
B The minimum diameter required for any appliance
Before connecting the gas supply, check the rating
plate on the right side of the heater to be sure that the
heater is rated for the same gas to which it will be
connected.
In the United States: The installation must conform with
local codes or, in the absence of local codes, the
National Fuel Gas Code ANSI Z223.1/NFPA 54.
In Canada: The Installation should conform to CGA
B149 INSTALLATION CODES and/or local installation
codes.
connector used is ¾”.
B National Fuel Gas Code requires that a sediment
trap (drip leg) be installed on gas appliances not so
equipped. The drip leg must be accessible and not
subject to freezing conditions. Install in accordance
with the recommendations of the serving gas
supplier.
When connections are made, check for gas leaks at all
joints. Apply some gas leak detection solution to all gas
fittings. Bubbles are a sign of a leak. A combustible gas
detector may also be used to detect for leaks.
Mount regulator to gas inlet pipe as shown in Fig. 13.
The arrow on the back of the regulator indicates the
direction of gas flow and should point toward the
appliance.
Danger: If you have a leak, shut off the
gas. Tighten appropriate fittings to stop
leak. Turn the gas on and check again
with a gas leak detection solution.
Never test for gas leaks using a match
or flame.
HIGH ALTITUDE INSTALLATION
The pressure regulator provided with the heater is
adjusted to deliver the proper gas pressure (as
indicated on the rating plate and in the manual for
altitude up to 2000 feet (660 meters) above sea level.
On appliances being installed above 2000 ft (660
meters) elevation, the inlet gas pressure should be set
at installation to the value shown below.
Note: The gas pressures specified below refer to
pressures taken at the pressure tap on the gas inlet pipe
just above the regulator. See chapter 3.8 for measuring
gas pressure.
Fig. 13 Installation of Gas Pressure Regulator
Note: The GWH 425 PN comes with a gas pressure
regulator. Not installing or altering the gas pressure reg-
ulator will be a violation of CSA certification of the unit.
The regulator supplied with the heater is preset for the
gas shown on the rating plate to the correct pressure. It
is an appliance level regulator designed for (low inlet)
pressure (less than 1/2 Psig or 14" W.C.).
MAXIMUM INLET GAS FLOW PRESSURE SETTING
Nat. Gas
inches W.C.
Liquid Propane
inches W.C.
Altitude
0’ - 2 000 ft
5.7”
4.6”
10.5”
8.4”
Warning: DO NOT connect to an
unregulated or high pressure propane
line or to a high pressure commercial
natural gas line.
2 000 ft - 4 500 ft
Table 3 Above 4.500 ft consult your local gas provider
GAS LINE SIZING
The gas supply piping should be sized according to the
applicable code for a maximum draw of 117,000 BTUH.
Measure the length of gas supply line and use the tables
in Fig. 14 or the gas line manufacturer’s sizing tables to
determine the pipe diameter necessary to
accommodate the BTU demand of the unit. If there are
more gas appliances drawing on the same line, size the
gas line according to the total maximum amount of BTU
draw for all appliances.
Warning: The heater must be isolated
from the gas supply piping system
during any pressure testing of that
system at test pressures equal to or
more than 0.5 psig. If overpressure has
occurred, such as through improper
testing of the gas lines or malfunction of
the supply system, the gas valve must
be checked for safe operation.
Note: Under sizing the gas line may result in diminished
output and improper operation. See chapter 3.8 for the
procedure to confirm gas pressure.
GAS CONNECTIONS
B Install a manual gas shut off valve, on the gas supply
line.
B Install a union when connecting gas supply.
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Installation instructions
FOR NATURAL GAS
Maximum Capacity of pipe in Cubic Feet of Gas per Hour for Gas Pressure of 0.5 Psig or less and a Pressure drop
of 0.3 in Water Column (0.75mbar).(Based on a 0.60 Specific Gravity Gas) Btu numbers given in thousands.
Copper tubing is prohibited for use with Natural Gas in the Commonwealth of Massachusetts and not recommended
elsewhere.
Follow boxed numbers for piping just one GWH 425 PN (example: ¾” B.I. Natural Gas pipe for 20 ft (6.1m). will
handle 190,000 btu’s (55.7 kWh). For multiple appliances combine the total btu input load and then refer to
applicable chart below.
Nominal
Iron
Pipe
Size
Length of Black Iron Pipe, Feet
Internal
Diameter
inches inches
10
20
30
40
50
60
70
80
90
90 100 125 150 175 200
84 79 72 64 59 55
3/4
1
0.824
1.049
278 190 152 130 115 105 96
520 350 285 245 215 195 180 170 160 150 130 120 110 100
1 1/4
1.380 1050 730 590 500 440 400 370 350 320 305 275 250 225 210
Length of Flexible Corrugated Stainless Steel Tubing (CSST), Feet
Tube
size,
inches
EHD*
10 20
30
47
96
40
41
50
37
60
34
1/2
18 EHD 82 58
23 EHD 161 116
3/4
1
83
75
68
* EHD = Equivalent Hydraulic Diameter. The greater the
value of EHD, the greater the gas capacity of the tubing
30 EHD 330 231 188
162
325
144
292
131
267
.
1 1/4 37 EHD 639 456 374
FOR LP GAS
Maximum Capacity of Pipe in Thousands of BTU per Hour of Undiluted Petroleum Gases (at 11 inches Water Column Inlet
Pressure) (Based on a Pressure Drop of 0.5 Inch Water Column).
* EHD = Equivalent Hydraulic Diameter. The greater the
value of EHD, the greater the gas capacity of the tubing.
N ominal
Iro n pipe
size
Length of Flexible Corrugated Stainless Steel Tubing (CSST), Feet
Tube
Black Iron Pipe
Lenght of pipe, Feet
size
inches
EHD*
inches
10 20 30 40 50 60 80 100 125 150 200
10 20
30
74
40
50 60
1/2
3/4
1
18 EHD 129 91
64
58 53
118 107
227 207
1/2
3/4
291 200 160 137 122 110 94 84
74
67
58
608 418 336 287 255 231 197 175 155 140 120
1145 787 632 541 480 434 372 330 292 265 227
23 EHD 254 183 151
30 EHD 521 365 297
131
256
1
1 1/4 37 EHD 971 661 528
449
397 359
Maximum Capacity of Semi-Rigid copper Tubing in
Thousands of BTU per Hour of Undiluted Liquefied
Petroleum Gases (at 11 inches Water Column Inlet
Pressure).
Copper (LP gas only)
Length of Tubing, Feet
Outside
diameter
Inch
10 20 30
39 26 21
92 62 50
40
19
41
50 60 70 80 90 100
3/8
1/2
_
_
_
_
_
_
(Based on a Pressure Drop of 0.5 Inch Water Column)
37 35 31 29 27 26
79 72 67 62 59 55
* Source National Fuel Gas Code NFPA 54, ANSI Z223.1
- No Additional Allowance is necessary for an ordinary
number of fittings
5/8 199 131 107 90
3/4 329 216 181 145 131 121 112 104 95 90
Fig. 14
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Installation instructions
Although water piping throughout your structure may be
other than copper, we recommend that copper piping
or suitably rated stainless steel flex line piping be used
for at least three feet before and after the heater (follow
local codes if more stringent). Never sweat any rigid
piping directly to or beneath the water connections,
damage can occur to the internal water valve from
heating of the pipe. Plastics or other PEX type plumbing
line materials are not recommended for connecting
directly to the water heater. Keep water inlet and outlet
pipes to no less than ½" (12.7mm) diameter to allow the
full flow capacity.
3.8 Measuring gas pressure
Connecting manometer
B Shut off gas.
B Remove front cover and locate inlet gas pressure
measuring point on the right side, see Fig. 15.
B Loosen screw from test point on the right side and
connect manometer tube on test point.
It is recommended that all water piping below the heater
be properly insulated to avoid heat loss.
If the cold and hot connections to the heater are
reversed, the heater will not function. Be certain there
are no loose particles or dirt in the piping. Blow out or
flush the lines before connecting to the water heater.
Full port valves should be installed on both the cold
water supply and hot water outlet lines to facilitate
servicing the heater (see Fig. 16). For installation on a
private well system with the use of a pressure tank, the
lowest pressure range setting recommended is 30-50
psi (2.07 and 3.45bar).
Connecting the pressure relief valve (PRV)
The pressure relief valve supplied with the heater must
be installed at the time of installation. No valve is to be
placed between the PRV and the heater. No reducing
coupling or other restriction may be installed in the
discharge line. The discharge line must be a minimum of
4” above a drain and installed such that it allows
complete drainage of both the PRV and the line.
The location of the PRV must be readily accessible for
servicing or replacement, and be mounted as close to
the water heater as possible. See Fig. 16. To install the
PRV, a suitable fitting connected to an extension on a
“T” fitting can be sweated to the hot water line.
Support all piping.
Fig. 15 Gas pressure measuring point
A
Inlet tap
Static pressure test
B Turn gas supply back on.
B Record static gas pressure reading on back page of
manual.
Operating pressure test
B Turn on all hot water taps served by the water heater.
B Run high hot water flow rate.
B Set flow control knob fully clockwise.
B Set slide control to the right.
B Record operating gas pressure reading on back
page of manual.
Gas pressures lower than 5.7" W.C. for Natural Gas or
10.5" W.C. for LP Gas will result in insufficient degree
rise to the hot water being used, and must be corrected.
See Gas Line Sizing under chapter 3.7.
3.9 Water connections
When facing the heater, the ½” cold water inlet is on the
bottom right and the hot water outlet is on the bottom
left.
B Install unions or the Webstone service valves
when connecting plumbing to the water
heater. This will facilitate any necessary
cleaning and servicing.
Fig. 16 Plumbing connections and pressure relief
valve shown with optional Webstone service
valves
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Operation instructions
3.10 Recirculation application
4
Operation instructions
Since recirculation through the heater is not
permissible, the following drawing is provided to outline
a proper recirculation application using the BOSCH
PRO water heater with an Ariston minitank. This
schematic is for illustration only and must not be used
for actual installation without appropriate engineering
and technical advice from a professional properly
licensed in locality where the installation is made.
4.1 For your safety read before
operating your water heater
Warning: If you do not follow these
instructions exactly, a fire or explosion
may result causing property damage,
personal injury or loss of life.
Note: Upon initial installation,
existence of air in the gas supply
i
line and in the water line may
cause some ignition delay. In that
case, repeat the ignition process
until all the air has been purged.
A. This appliance employs a piezo-igniter to light the
pilot burner. When lighting the pilot, follow these
instructions exactly.
B. What to do if you smell gas.
Fig. 17 Recirculation application
WHAT TO DO IF YOU SMELL GAS
The use of a small electric mini-tank (4-6 gallon size)
should be used for this application and designed so the
pump will circulate the water through the mini-tank and
the building's hot water return loop only. A timed or
thermostatically controlled operation of the pump is
commonly done. The GWH 425 PN should be plumbed
in line before the mini-tank water heater. Contact Bosch
Water Heating if further instruction is needed.
B Close gas valve. Open windows.
B Do not try to light any appliance.
B Do not touch any electric switch; do not use any
phone in your building.
B Immediately call your gas supplier from a neighbors
phone. Follow the gas supplier’s instructions.
B If you cannot reach your gas supplier, call the fire
department.
C. Use only your hand to push in the gas control
buttons. Never use tools. If a button will not push in,
check to make sure the buttons are being pushed in the
proper sequence. Follow these instructions exactly. If
control button(s) are jammed, close the heater’s
individual manual shutoff valve and call a qualified
service technician. Forced or attempted repair may
result in a fire or explosion.
D. Do not use this appliance if any part has been under
water. Immediately call a qualified service technician to
inspect the appliance and to replace any part of the
control system and any gas control which has been
under water.
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Operation instructions
B With the gas valve button fully depressed, light pilot
by pushing the piezo button. This step may have to
be repeated.
4.2 Lighting instructions
B STOP! Read the previous safety information.
B The gas valve must be turned off by sliding the gas
valve button to all the way to the left.
Fig. 18
Fig. 21
B Wait five (5) minutes to clear out any gas. If you smell
gas, STOP! Follow “B” in chapter 4.1. If you don’t
smell gas, go to next step.
B Observe the pilot flame through the peephole. The
gas valve button should be held down for at least 15
seconds with pilot burning before releasing. When
the gas valve button is released, the pilot should
continue to burn.
B The pilot burner window is located in the front center
of the cover.
- If the gas valve button does not pop out when
released, stop and immediately call your service
technician or gas supplier.
B Slide the gas valve button to the position
.
- If pilot does not stay lit, repeat all steps.
- If pilot will not stay lit after several tries, slide the gas
valve button all the way to the left and call service
technician or gas supplier.
B The heater will now fire at minimum power when
water is drawn at a rate greater than the required
activation flow rate.
Note: If main burner should fail to ignite, make sure pilot
is burning. If not, repeat lighting steps.
Note: The GWH 425 PN operates in two modes. See
SETTING THE WATER TEMPERATURE.
Fig. 19
B Fully depress gas valve button.
4.3 To turn off appliance
B Slide the gas valve button all the way to the left and
turn off the installer supplied manual gas shutoff on
the supply line to the heater.
Fig. 20
Fig. 22
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Operation instructions
The hottest position is the highest flame position all the
way to the right.
4.4 Setting the water temperature
The GWH 425 PN has a gas control that modulates
burner input in response to flow. Its purpose is to
ensure that the hot water temperature will remain
steady, although the water flow demand might vary. The
output temperature can be adjusted with either the
temperature adjustment knob or the gas control slide.
Temperature adjustment knob
The temperature adjustment knob on the front bottom of
the heater (see Fig. 23) adjusts temperature by
adjusting flow capacity. See table 4 for details.
Fig. 25
4.5 Draining water from heater
If there is a risk of freezing, proceed as follows:
B Remove the retaining clip from threaded bushing
(pos. 1).
B Remove threaded bushing (pos. 2) from water valve.
B Empty the appliance of all water.
Fig. 23
Knob
position
Counter-
clockwise
Clockwise
Degree rise
90°F
45°F
Activation rate
Max flow rate
0.5 GPM
2.0 GPM
1.1 GPM
3.7 GPM
Table 4 Temperature rise (slide control to the right)
As the temperature adjustment knob is turned counter-
clockwise, the output temperature will lower and the
activation rate will be raised. Turning the knob
clockwise will raise the temperature and lower the
activation rate.
Fig. 26 Drain plug and filter location
Gas control slide button
1
2
Retaining clip
Threaded bushing
The gas control slide button adjusts temperature by
adjusting how much gas is allowed to flow to the
burners.
As the slide is adjusted to the left, the output
temperature will lower, with the lowest setting being the
small flame position.
Fig. 24
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Maintenance and service
5
Maintenance and service
clip on water valve assembly and pulling the pipe free
from the water valve. Loosen the two set screws at the
bottom of the water valve where it connects to the gas
valve. If the set screws are seized, STOP and call
Bosch tech support before proceeding. Forcing and
snapping seized set screws may cause irrevocable
damage to the water valve and gas valve assemblies.
Remove the water valve by pulling it to the right.
Separate the two halves of the water valve by removing
the five screws on the left side of the water valve. Apply
lithium or faucet & valve grease to the pushrod and o-
ring. (See Fig. 29). Inspect the venturi and clean if
necessary. (see Fig 29).
5.1 Maintenance intervals
Warning:
Failure
to
perform
recommended maintenance may result
in complete failure of the unit over time.
The warranty does not cover failures
due to improper or insufficient
maintenance.
The GWH 425 PN requires periodic maintenance. The
below time maintenance intervals should kept the unit
operating for many years.
Every year
Rebuilding the water valve
B Inspect inlet water filter screen ( 5.2)
B Inspect pilot assembly and flame ( 5.3)
B Inspect burner assembly ( 5.4)
Several parts within the water valve should be replaced
every 3 to 5 years depending on water quality and
usage. The parts list and instructions can be found on
the water valve can result in decreased performance or
damage to the heater.
Every 2 years
B Lubricate and clean water valve ( 5.2)
Every 3 to 5 years
5.3 Pilot
B Rebuild water valve ( 5.2)
Inspecting pilot
B Clean pilot assembly and clean or replace orifice
The pilot should burn with a clean sharp blue flame. The
flame should fully engulf the tip of the thermocouple. If
it does not, clean the pilot assembly per procedure
below.
( 5.3)
5.2 Water valve
The water valve is the main control that tells the heater
to fire. If the periodic maintenance is neglected, more
costly damage may occur over time.
Cleaning pilot assembly
Shut off gas supply to the heater using installer supplied
manual gas shutoff. Locate pilot gas tubing mounted in
the center of the burner assembly. At the base of the
pilot gas tubing there is a retaining clip. Release pilot
gas tubing from this clip. Push upwards on other end of
pilot gas tubing to release it from burner mount.
Remove brass hex headed pilot orifice from gas valve
(located near base of pilot gas tubing). Soak orifice and
pilot gas tubing in carburetor cleaner for 30 minutes.
Dry off and reinsert orifice in gas valve. If heater is an LP
unit, replace orifice. Reinstall the pilot gas tubing
following removal instructions in reverse. Open gas
supply and return heater to service.
Inspecting inlet water filter screen
Shut off the installer supplied cold water isolation valve
to the heater. If one is not installed, install before
proceeding. Open the nearest hot water tap to drain the
plumbing lines. Position a bucket under the heater's
water valve assembly to catch any water that may drain
from the heater. Remove the filter retaining clip located
at base of water valve (see Fig. 26). Remove the
threaded bushing to access the cylindrical filter inside.
Remove filter, clean with water and inspect for damage.
If the filter is at all damaged, it should be replaced.
Lubricating the water valve
Caution: Do not ream or poke orifice as
it will enlarge orifice opening.
A more detailed instruction is available on our website
cold water isolation valve to the heater. If one is not
installed, install before proceeding. Open the nearest
hot water tap to drain the plumbing lines. Position a
bucket under the heater's water valve assembly to catch
any water that may drain from the heater. Disconnect
the inlet water pipe going to the back of the water valve.
Disconnect the water pipe leading out of water valve to
the heat exchanger. Do this by removing the retaining
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Maintenance and service
12. Run solution through the heat exchanger until the
solution returning to the descaling reservoir comes out
clear. (Changing to a fresh solution may be necessary
during this process).
5.4 Main burners
The main burner flames should be blue, with a more
intense blue cone in the center core. Yellow flames
could be a sign of wrong size gas orifices or dirty
burners, a blockage on the heat exchangers fins. If
some burners have yellow flames while others have blue
flames, it is likely that dust, lint or spider webs have
partially clogged the burner venturis. To clean the
burners, contact a gas service person.
13. Disconnect all lines and drain all solution from heat
exchanger. Properly discard of solution
14. Position a container below the hot water outlet and
connect cold water supply. Open cold water supply
isolation valve and flush heat exchanger with clean
water.
15. Shut cold water isolation valve and reconnect hot
water supply to the water heater.
5.5 Vent assembly
Inspect the draft hood and heat exchanger fins for signs
of soot build-up or any other foreign material such as
spider webs. Clean out any debris found in the vent
hood. Signs of soot indicate insufficient combustion air
or exhaust draft. Check for vent assembly blockage or
combustion air blockage on the underside of the unit.
16. Reconnect electrical supply to unit, open water
isolation valves, and return the unit to service.
5.6 Mineral scale build-up
The GWH 425 PN, when operated at lower
temperatures settings, does not accumulate mineral
build-up. If however, the heater is used at the higher
temperature settings and the water has a high mineral
content, periodic descaling may be necessary. The
heating coils should be flushed with a descaling
solution.
5.6.1 Descaling heat exchanger
1. Disconnect electrical supply from the water heater.
2. Shut off the water supply to the water heater using
(installer supplied) isolation valve.
3. Open hot water taps to drain and relieve pressure
from the plumbing system
Fig. 27
4. Drain water from the unit's heat exchanger by
disconnecting inlet and outlet water connections
5. Connect the line (A) from the outlet of the circulating
pump (installer supplied) to the inlet water fitting on the
water heater
6. Using another line (B), connect to the water outlet
fitting on the water heater. Route the other end of this
line into a descaling reservoir
7. Using a 3rd line (C) from the descaling reservoir,
connect to the inlet side of circulating pump. Verify
there is a filter on the end of the line in the descaling
reservoir.
8. Make sure all connections are "hand tight."
9. Fill tank with descaling solution so lines inside are
submersed. We recommend a straight white vinegar
solution. If using a commercial descalant, refer to
manufacturer's instructions on dilution with water.
10. Operate the circulating pump.
11. Make sure there are no leaks and the solution is
flowing from the descaling reservoir through the heat
exchanger and returning to the reservoir.
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Troubleshooting
6
Troubleshooting
electromagnet (See parts diagram for locations). Clean
sensor connections with light sandpaper if corrosion is
evident. The electromagnet connection is 5mm nut from
the thermocouple which screws into a larger 17mm nut.
Tighten both nuts snugly but do not over tighten.
6.1 Introduction
Many of the questions customers ask regarding
operation of this unit can be answered by following the
troubleshooting steps as outlined below. Visit our web
troubleshooting. For best results, perform each step
before proceeding to the next. The suggested solutions
may require that the cover be taken off. (See chapter
3.4).
5. Pilot flame should be blue in color and completely
engulfing the tip of the thermocouple. If not, have a
licensed gas technician verify gas pressure is in
accordance with manufacturer's specifications
(chapter 3.9) and clean or replace the pilot orifice
(chapter 5.3).
6.2 Pilot does not light
6. Have a licensed gas technician verify the proper
operation of the thermocouple by measuring the
millivoltage from the thermocouple lead to ground. The
proper reading should be 24mVDC or greater. If the
reading is lower, the thermocouple may be defective.
Call Bosch Water Heating for further instructions.
1. Verify gas supply is on at Natural Gas meter or
Propane Tank. Make sure all manual gas shut off valves
are in the open position. Have licensed gas technician
confirm adequate gas pressure at the inlet tap
(chapter 3.9). If gas is not present, verify manufacturer
supplied Maxitrol regulator is in the upright position. The
arrow on the back of the regulator should point in the
same direction as gas flow.
6.4 Pilot goes out during or after hot
water use
2. If the unit was just installed or the gas lines have been
worked on, there may be air in the gas line. Centered in
the sparking position, hold down the gas control slide
button while hitting the pilot igniter button every few
seconds. It may take several minutes to bleed air out of
the gas line.
1. Pilot outage during use typically results from the
unit's safety overheat/high limit sensors interrupting the
pilot circuit. The GWH 425 PN does not have a
thermostat. If inlet water is preheated, the unit will
overheat, stopping the flow of gas. Plumb inlet with a
cold water line only.
3. Verify a spark is being thrown at pilot area while gas
control slide button, centered in the single flame
position, is being firmly depressed. Repeatedly push in
pilot igniter button to light the pilot. If no spark is
present, verify proper wire connection to the electrode.
2. Failure to vent properly by reducing pipe diameter,
improper use of elbows or not meeting required vent
length are common causes that deactivate the pilot
safety circuit. Confirm venting is in accordance with
manufacturer's specifications (see chapter 3.7).
4. Pilot assembly may be blocked. Clean or replace the
pilot orifice (chapter 5.3).
3. Confirm the combustion air requirements are being
met in accordance with manufacturer's specifications
(see chapter 3.6). Proper venting and combustion air
will ensure a proper draft.
6.3 Pilot lights, but goes out when
button is released
4. Confirm that the burners in the water heater go off
immediately when the hot water is turned off. If they
remain on or shut down slowly, then the overheat
sensor (ECO) will interrupt the pilot circuit and shut off
all gas to the heater. The water valve assembly, which
actuates the burners, may be dirty and require periodic
maintenance (every 2 - 5 years depending on water
quality and use) (see chapter 5.2).
1. When lighting pilot ensure the gas control slide
button is fully depressed and held down for at least 20
seconds after pilot is lit.
2. Verify gas type indicated in rating sticker located on
right hand side of cover, coincides with the gas type you
are using. NG is a natural gas unit and LP is for liquid
propane.
5. Check all connections of the pilot safety circuit. The
pilot safety circuit consists of a thermocouple, overheat
sensor (ECO), flue gas sensor, safety spillage
switch(models with Powervents only) and the
electromagnet (See parts diagram for locations). Clean
sensor connections with light sandpaper if corrosion is
evident. The electromagnet connection is 5mm nut
from the thermocouple which screws into a larger
17mm nut. Tighten both nuts snugly but do not over
tighten.
3. If using a power vent, check the safety spillage switch
reset button (the safety spillage switch is wired through
the water heater's thermocouple circuit). The spill
switch should be located at top of water heater close to
draft diverter (Consult manual that came with
powervent).
4. Check all connections of the pilot safety circuit. The
pilot safety circuit consists of a thermocouple, overheat
sensor (ECO), flue gas sensor, safety spillage
switch(models with Powervents only) and the
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Troubleshooting
6. Verify pilot flame completely engulfs the
thermocouple tip. If pilot is too small, clean pilot orifice
(see chapter 5.3).
2. Check for a clogged inlet water filter screen (see
chapter 5.2).
3. Hot water is very hot out of the tap, requiring a lot of
cold water to be added with it in order to attain a
useable hot water temperature. The addition of too
much cold will overpower and slow the flow within the
tankless water heater, decreasing it below activation
point, which shuts off the burners. The end result is
nothing but cold water coming out of the outlet.
Reduce the need for cold water mix by setting the gas
slide control button towards the single flame position
for lower hot water temperatures. If the problem
service bulletin on this problem.
7. If the water has a high mineral content, the heat
exchanger may be scaled internally. This restricts the
water path, causing the water to over heat which shuts
all gas off to the heater. Instructions for descaling the
8. If steps 1 through 7 do not correct the problem, then
confirm that the gas pressure is adequate. Ensure gas
pressure is in accordance with manufacturer's
specifications (see chapter 3.9). A gas pressure
reading is needed to proceed further. Contact your
original installer or a licensed gas technician to obtain
this reading.
4. The GWH 425 PN is designed to modulate gas flow
to the burners when water flow varies. If the water
pressure in the home is erratic and the water flow is not
consistent while a tap is opened, then the temperature
of hot water will fluctuate. The minimum water pressure
for the home should be 30psi or greater. For installation
on a private well system with the use of a pressure tank,
the lowest pressure range setting recommended is 30-
50 psi (2.07-3.45 bar). The use of a pressure reducing/
regulating valve before the water heater (directly after
pressure tank on well systems) is an effective way to
maintain constant water pressure to the water heater.
Watts brand 25AUB- ¾" or N35B-¾" pressure
reducing/regulating valves or equivalent are suggested.
6.5 Burners do not light with water
flow
1. Verify the pilot is lit.
2. Verify the gas control slide button is in middle
position.
3. Verify the cold water supply is connected to the right
side of the heater.
4. Close installer supplied cold water shut off valve (if
none installed, install before proceeding). Open all hot
water taps supplied by the heater. Wait 5 minutes and
check all taps. Any water running is a sign of a plumbing
crossover. Consult a local plumber or service person for
help in correcting a plumbing crossover.
5. If the inlet water temperature is not steady then the
hot water temperature from the water heater will
fluctuate. The GWH 425 PN modulates its burners
when the flow rate is changed; it does not have a
thermostat and will not adjust to changes in inlet water
temperature.
5. Verify flow through the water heater is sufficient. Turn
temperature adjustment knob all the way clockwise.
Fully open a hot water faucet and fill a quart container.
If the container fills in 30 seconds or less, the flow rate
(1/2 gallon per minute) is sufficient to activate the
heater.
6. If the inlet water temperature to the water heater is
above 70°F, the heater may produce outlet
temperatures that are too hot for most users. A
temperature balance shower valve can automatically
mix in cold water to reduce such hot water temperature.
This can slow the flow within the tankless water heater,
decreasing it below activation point, which shuts off the
burners. In the event of any temperature instability with
the use of a temperature balance shower valve, refer to
shower valve manufacturer's instructions for internal
adjustment setting. An adjustment should be made to
minimize the amount of cold water the valve is adding.
6. Inspect the water path outside of the heater for
obstructions. Make sure all outlets (i.e. showerheads,
faucet aerators and whole house filters) are clear of
debris. Also, the water heater's inlet filter screen should
be inspected and cleaned (see chapter 5.2).
7. The water valve assembly, which actuates the
burners, requires periodic maintenance (every 2 - 5
years depending on water quality and use) (see
chapter 5.2).
7. The gas pressure also needs to be stable and
adequate. Ensure gas pressure is in accordance with
manufacturer's specifications (see chapter 3.9). A gas
pressure reading is needed to proceed further. Contact
your original installer or a local certified gas technician
to obtain this reading.
6.6 Hot water temperature fluctuates
at tap
1. Close off installer supplied cold water shut off valve
(if none installed, install before proceeding). Open all
hot water taps supplied by the heater. Wait 5 minutes
and check all taps. Water running is a sign of a
plumbing cross-over. Consult a local plumber or service
person for help in correcting a plumbing crossover.
8. A water valve, which has not been serviced, may be
struggling to keep the gas valve open. The water valve
requires periodic maintenance (every 2-5 yrs
depending on water quality and use) (see chapter 5.2).
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Troubleshooting
faucet aerators and whole house filters) are clear of
debris. Also, the water heater's inlet filter screen should
be inspected and cleaned (see chapter 5.2)
6.7 Water is too hot
1. Verify gas type indicated in rating sticker located on
right-hand side of cover, coincides with the gas type
you are using. NG is a natural gas unit and LP is for
liquid propane.
6. The water valve may be dirty, prohibiting it from fully
opening the gas valve. This part needs to be periodically
serviced (every 2-5 yrs depending on water quality and
use) (see chapter 5.2).
2. Adjust the gas control slide button from three flame
position towards the one flame position for cooler
7. Gas pressure is too low. Ensure gas pressure is in
accordance with manufacturer's specifications (see
chapter 3.9). A gas pressure reading is needed to
proceed further. Contact your original installer or a local
certified gas technician to obtain this reading.
temperatures.
If the water is still too hot, the
temperature adjustment knob on the water heater
maybe set too high. Lower the setting and test water
temperature. This dial turns counter clockwise for lower
temperatures and clockwise for higher temperatures.
3. Inlet water is preheated. This model does not have a
thermostat and thus will not modulate flame height in
order to prevent over heating. It is designed for a cold
water feed only. Replumb the heater with cold water to
the inlet.
6.9 Burners ignite without hot water
flow
1. The water valve may be dirty and sticking, prohibiting
it from fully closing the gas valve. This part needs to be
periodically serviced (every 2-5 yrs depending on water
quality and use) (see chapter 5.2).
4. Increase the flow rate. Restrictions in the water path
can slow the flow of water through the heater, resulting
in very hot outlet temperatures. Restrictive
showerheads and faucet aerators should be cleaned
out or upgraded with less restrictive ones. In addition,
the water heater's inlet filter should be cleaned and
inspected (see chapter 5.2).
6.10 Low hot water pressure
1. Confirm adequate flow rate through the unit. With
cold supply shut off to the unit, disconnect hot outlet
side to the unit. Place a half gallon jug under hot outlet
to catch water. Open cold supply and measure flow rate
out of the unit. With temperature adjustment knob set all
the way clockwise, the flow rate should be close to
2gpm, filling the jug in 15 seconds. With the
temperature adjustment knob set all the way
counterclockwise, the flow rate should be close to
4gpm, filling the jug in 7 seconds. If the flow rate is not
adequate, inspect and clean the inlet filter screen (see
chapter 5.2).
5. If water is still too hot, consult service bulletins on
further.
6. If the water has a high mineral content, the heat
exchanger may be scaled internally. This restricts the
water path, causing the water to boil and produce
extremely hot temperatures. Instructions for descaling
the
heat
exchanger
are
available
at
2. Confirm the incoming water pressure to the unit is
above the required 30psi.
6.8 Water is not hot enough
1. Verify gas type indicated in rating sticker located on
right-hand side of cover, coincides with the gas type
you are using. NG is a natural gas unit and LP is for
liquid propane.
3. Inspect the water path outside of the heater for
obstructions. Make sure all outlets (i.e. showerheads,
faucet aerators and whole house filters) are clear of
debris.
2. Flow at one particular tap is too great or too many
fixtures are running at one time. Lower flow to stay
within heater's specifications.
4. Be sure to run only one major application at a time
with this unit. Opening too many taps at one time can
disperse water flow resulting in a diminished flow/
pressure at all outlets.
3. Ensure the gas control slide button is all the way to
the right. In addition, the temperature adjustment knob
on water heater maybe set too low. Turn the knob
clockwise for higher temperatures and test the water
temperature.
5. If the water has a high mineral content, the heat
exchanger may be scaled internally. This restricts the
water path, causing diminished water flow. Instructions
for descaling the heat exchanger are available at
4. Shut off installer supplied cold water shut off valve (if
none installed, install before proceeding). Open all hot
water taps supplied by the heater. Wait 5 minutes and
check all taps. Any water running is a sign of a plumbing
crossover. Consult a local plumber or service person for
help in correcting a plumbing crossover.
6.11 Noise when heater is running
1. Confirm adequate flow rate through the unit. With
cold supply shut off to the unit, disconnect hot outlet
side to the unit. Place a half gallon jug under hot outlet
to catch water. Open cold supply and measure flow rate
out of the unit. With temperature adjustment knob set all
5. Inspect the water path outside of the heater for
obstructions. Make sure all outlets (i.e. showerheads,
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Troubleshooting
the way clockwise, the flow rate should be close to
2gpm, filling the jug in 15 seconds. With the
temperature adjustment knob set all the way
counterclockwise, the flow rate should be close to
4gpm, filling the jug in 7 seconds. If the flow rate is not
adequate, inspect and clean the inlet filter screen (see
chapter 5.2).
2. Inspect the water path outside of the heater for
obstructions. Make sure all outlets (i.e. showerheads,
faucet aerators and whole house filters are clear of
debris. Restrictions in the water path can slow water
flow through the heat exchanger causing it to boil and
make noise.
3. If the water has a high mineral content, the heat
exchanger may be scaled internally. This restricts the
water path, causing the water to boil resulting in noise
and overheating. Instructions for descaling the heat
6.12 Burners do not operate cleanly;
yellow flames when operating
1. Verify gas type indicated in rating sticker located on
right-hand side of cover, coincides with the gas type
you are using. NG is a natural gas unit and LP is for
liquid propane.
2. Gas pressure may be inadequate resulting in
improper combustion. Ensure gas pressure is in
accordance with manufacturer's specifications (see
chapter 3.6). A gas pressure reading is needed to
proceed further. Contact your original installer or a
licensed gas technician to obtain this reading.
3. For proper combustion at high elevations the inlet
gas pressure should be set at installation to the value
shown in table 3 (while operating at maximum BTU). A
gas pressure reading is needed to proceed further.
Contact your original installer or a licensed gas
technician to obtain this reading.
4. Ventilation is not adequate. Ensure adequate
combustion air is being supplied to the unit in
accordance with manufacturer's specifications (see
chapter 3.6).
5. Make sure the water heater is vented properly. Check
for proper draft and ensure venting is in accordance
with manufacturer's specifications (see chapter 3.7).
6. The water heater has burners much like a furnace. It
is essential that they remain clean and are supplied with
adequate air for combustion. If the flames burn yellow or
orange, it is strongly recommended that the burners be
removed from the unit and cleaned. Once the burners
are removed, the fins in the top of the heat exchanger
can be accessed and brushed or vacuumed clean.
Instructions to remove burners are available at
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Protecting the environment
7
Protecting the environment
Packing
The packing box may be fully recycled as confirmed by
the recycling symbol
.
Components
Many parts in the heater can be fully recycled in the end
of the product life. Contact your city authorities for
information about the disposal of recyclable products.
Saving water resources:
B Make sure you close all the taps after any use. Avoid
leaving the taps dripping. Repair any leaking tap.
B Set the water heat to the temperature you want. This
way you have the precise water flow needed (mixing
cold water to regulate temperature will increase the
water flow with consequent waste of water).
For increased safety shut off the appliance from
the main water supply if your are staying away
from home for a considerable time.
At below freezing temperatures, disconnect the
plumbing connections to the heater and allow
the heater to drain.
To prevent any freeze damage, introduce short
bursts of compressed air (20-40 psi) through
these connections to remove the residual water
in the horizontal pipes and water valve.
Follow instructions in chapter 4.5 to remove any
additional water remaining in the watervalve and
heat exchanger.
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Interior components and diagram parts list
8
Interior components and diagram parts list
8.1 Interior components
Fig. 28 Functional scheme
4
5
10
11
20
Heat exchanger
Burner
Temperature adjustment selector
Water valve
22
26
30
102
Flexible hot outlet
Gas control slide
Pilot gas tubing
Piezo
Gas connection
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Interior components and diagram parts list
8.2 Components diagram
5
4
6
44
8
41
48
50
47
39
12
14
19
13
18
15
9
10
43
11
16
20
24
51
21
23
27
52
22
7
38
28
30
17
25
35
31
26
13
29
32
45
46
49
42
34
36
37
2
1
40
3
33
6720608126-02.1 JF
Fig. 29 Components Diagram
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Interior components and diagram parts list
8.3 Parts list
Item
Description
Reference
1
Front cover
8 705 431 246 0
8 705 506 817 0
8 702 000 295 0
8 705 505 442 0
8 705 504 046 0
8 708 003 192 0
8 701 103 135 0
8 705 406 275 0
8 700 715 061 0
8 708 120 618 0
8 708 120 619 0
8 705 209 062 0
8 701 201 019 0
8 748 107 089 0
8 700 707 369 0
8 740 609 002 0
8 700 507 067 0
8 707 021 396 0
8 707 021 395 0
8 705 502 067 0
8 701 004 044 0
8 708 200 326 0
8 708 200 327 0
8 708 500 301 0
8 708 500 358 0
8 708 500 359 0
8 707 201 028 0
8 703 305 283 0
8 708 008 069 0
8 701 000 380 0
8 707 406 083 0
8 707 406 084 0
8 707 006 344 0
8 703 204 051 0
8 700 503 084 0
8 700 306 110 0
8 708 500 304 0
8 708 108 051 0
8 701 302 181 0
8 704 401 040 0
8 707 202 083 0
8 707 206 445 0
8 701 004 043 0
8 700 103 658 0
8 700 306 148 0
8 700 306 187 0
8 700 507 059 0
8 700 703 139 0
8 701 201 020 0
8 703 502 039 0
8 705 705 034 0
8 707 206 017 0
8 707 206 132 0
8 708 205 279 0
8 700 715 178 0
8 700 715 351 0
8 705 500 105 0
2
Shield
3
Temp control knob
Draft Diverter
4
5
Exhaust pipe union Ø128
Angle bracket
6
7
Trade mark badge
Heat exchanger
Cold water pipe
Main burner NG
Main burner LP
Connector
8
9
10
10
11
12
13
14
15
16
17
17
18
19
20
20
21
22
22
23
24
25
26
27
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
Piezo clip (x10)
Sparking plug
Pilot gas pipe
Tube (x10)
Pilot screen
Gas valve LP
Gas valve NG
Throttle housing
Washer (x10)
Pilot injector LP
Pilot injector NG
Pilot valve
Poppet valve head (2) NG
Poppet valve head (3) LP
Electromagnet
Electromagnet cap
Valve operation housing
Guide plate
Gas pressure regulator LP
Gas pressure regulator NG
Water valve
Watervalve pushrod (10x)
Diaphragm (L)
Inlet water connection
Selector screw
Piezo igniter
Fixing bracket
Ignition lead
Thermocouple
Flue gas safety device
Washer (x10)
Heat exchanger washer
Threaded bushing
Connector
Water filter
Outlet Hose
Water connection clip
Plunger
Volumetric water governor
ECO
Temperature limiter
Venturi
Hot water pipe
Gas supply pipe
Cover
Table 5
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Fifteen Year Limited Warranty
9
Fifteen Year Limited Warranty
General
costs associated with service, removal or re-installation
of the original water heater or a replaced water heater.
BOSCH PRO water heaters are warranted by the
Manufacturer (BOSCH) through BBT North America.
BBT North America (BBTNA) will furnish a replacement
heat exchanger and will furnish a replacement of any
other part which fails in normal use and service within
the applicable periods specified below, in accordance
with the terms of this warranty. The BBTNA
replacement will be warranted for the unexpired portion
of the original warranty. This warranty will be valid only
for water heaters in possession of the original purchaser
as recorded on the warranty card.
Note: the water heater must be free of
damaging scale deposits and not subject
i
to gas pressures greater than those
shown on the rating plate, which must not
be altered, defaced or removed.
How to Make a Claim
Any claim for warranty parts should be made to your
local dealer, distributor or to BBTNA. If BBTNA, please
contact the Technical Support Department:
The Heat Exchanger
BBT NORTH AMERICA
Bosch Group
If the heat exchanger fails within fifteen (15) years after
the original installation and operation BBTNA will
furnish a replacement heat exchanger. However, if the
water heater is installed in other than a single family
dwelling this heat exchanger warranty is limited to two
(2) years from date of original installation and operation.
340 Mad River Park
Waitsfield, VT 05673
Phone: 866-330-2730
Exceptions
In most cases, the dealer or distributor will be able to
promptly honor your claim and subsequently notify
BBTNA. However, all replacements are made subject to
validation by BBTNA of in-warranty coverage. The
damaged or defective item must be made available in
exchange for the replacement.
This warranty will not apply:
1. to defects or malfunctions resulting from failure to
properly install, operate or maintain the unit in
accordance with the printed instructions provided;
2. to damage or abuse, accident, neglect or freezing
and other acts of nature;
Miscellaneous
3. to damage resulting from operation with either the
No one is authorized to make any other warranties on
behalf of BBTNA. It is expressly understood that the
replacement warranty of BBTNA shall be in lieu of any
and all other warranties, express or implied, including
warranties of merchantability or fitness for a particular
use or purpose, and further that BBTNA shall not be
liable for any loss or damage directly or indirectly arising
from the use of the hot water heater, or for any
consequential damages arising from such use
(including damages from water leakage). BBTNA sole
liability with respect to any defect shall be for the
replacement of the defective part(s). Some states do
not allow such limitations and exclusions, so the above
may not apply to you.
flame sensor rod or overheat sensor removed;
4. to failure of the heat exchanger resulting from the
operation of the water heater in a corrosive
atmosphere or at water temperatures exceeding the
maximum rating, or if the water heater is not supplied
with potable water;
5. to defects or damage cause by any attachment
or modification, including any energy-saving device.
All Other Parts
If any other part fails within two (2) years after original
installation and operation, BBTNA will furnish a
replacement part free of charge.
This warranty gives specific legal rights. You may also
have other rights which vary from state to state.
Shipping costs
In addition to supplying the replacement part(s),
BBTNA will provide ground service delivery for these
parts. Expedited or upgraded shipping will be charged
to the customer.
Service Labor Costs
This warranty does not cover any labor costs
associated with service, removal or re-installation of
part(s). All such costs must be borne by the Purchaser.
Additionally, this warranty does not cover any labor
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Installer Checklist, to be performed by installer upon installation
Serial Number
___ ___ ___ ___ ___ ___ ___ ___
(8 digit serial number is located on rating plate on right side panel)
Gas Pressure Reading*
Building Water Pressure
Average Winter Temperature
Average Summer Temperature
Installing Company
Installer name
Static__________
Operating__________
__________ Range if on Well system __________
__________
__________
_____________________________________________
_____________________________________________
_____________________________________________
_____________________________________________
Address
Phone
* See Chapter 3.8 and gas pressure table (to be filled out by installer)
Installation manual should be left with the owner after the installation is tested and completed
BBT NORTH AMERICA
Bosch Group
VULCANO Termodomésticos S.A.
Bosch Water Heating
Estrada de Cacia
340 Mad River Park
Waitsfield, VT 05673
Phone 866-330-2730
Fax 802-496-6924
3801 - 856 Aveiro - PORTUGAL
Recycled paper
© 2006 BBT NORTH AMERICA CORPORATION,
Waitsfield, VT all rights reserved
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