GWH-425-HNO-N
GWH 425 HNO OUTDOOR MODEL
For exterior use only
Electronic Ignition
Suitable for heating potable water only - Not approved for space heating purposes
GWH-425-HNO-N - Natural Gas
GWH-425-HNO-L - Liquefied Petroleum (LP) Gas
8 716 473 148 US (05.12) AL
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.
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.
In the Commonwealth of Massachusetts this
product is approved only for seasonal use.
Installation must be performed 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.
What to do if you smell gas
• Close gas valve.
• Do not try to light any appliance.
• Do not touch any electrical switch; do not use any
phone in your building.
• If you cannot reach your gas supplier, call the fire
department.
• Immediately call your gas supplier from a neighbor’s
phone. Follow the gas supplier’s instructions.
•
Installation and service must be performed by a
qualified installer, service agency or the gas supplier.
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Index
Index
1 Warning 2
2 Appliance details 4
2.1 Features 4
2.2 GWH-425-HNO specifications (Technical data) 4
2.3 Unpacking the GWH-425-HNO heater 5
2.4 General rules to follow for safe operation 5
2.5 Dimensions and installation clearances 6
3 Installation instructions 7
3.1 Introduction 7
3.2 Proper location for installing your heater 7
3.3 Heater placement and clearances 8
3.4 Mounting installation 8
3.5 Gas piping & connections 10
3.6 Measuring gas pressure 12
3.7 Water connections 12
3.8 Electrical connections 13
4 Operation instructions 14
4.1 For your safety read before operating your water
heater 14
4.2 Lighting instructions 14
4.3 To turn off appliance 14
4.4 Setting the water temperature 14
4.5 Electrical diagram 16
5 Maintenance and service 17
5.1 Maintenance intervals 17
5.2 Water valve 17
5.3 Pilot 17
5.4 Main burners 17
5.5 Vent assembly 17
5.6 Mineral scale build-up 17
6 Troubleshooting 18
6.1 Introduction 18
6.2 Pilot will not light 18
6.3 Pilot lights but the burners will not come on 18
6.4 Hot water temp fluctuates from hot to cold 18
6.5 Water is too hot 19
6.6 Water is not hot enough 19
7 Interior components diagram and parts list 20
7.1 Interior components 20
7.2 Components diagram 21
7.3 Parts list 22
8 Protecting the environment 23
9 Fifteen Year Limited Warranty 24
1 Warning
For your safety
Do not store or use gasoline or other flammable,
combustible or corrosive vapors and liquids in the
vicinity of this or any other appliance.
Warning: If the information in this
manual is not followed exactly, a fire or
explosion may result causing property
damage, personal injury or death.
Warning: 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.
Upon completion of the installation,
these instructions should be handed to
the user of the appliance for future
reference.
Warning: Carefully plan where you
install the heater. If a gas appliance is
not installed correctly, fatal accidents
can result from lack of air, carbon
monoxide poisoning or fire.
Warning: Place the heater in a location
where water leaks will do NO DAMAGE
to adjacent areas.
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Warning
3
What to do if you smell gas
• Close gas valve.
• 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.
• 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.
Fig. 1
Fig. 2
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.
Caution: Any changes or
modifications not expressly approved
by the party responsible for compliance
could void the user’s authority to
operate the equipment.
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Appliance details
2 Appliance details
2.1 Features
• Burner output proportional to hot water flow demand
for maximum energy efficiency
• Stainless steel burners with stabilized blue flame
• Built-in corrosion resistant draft diverter
• Adjustable water flow restrictor to ensure that water
flow demand will not exceed the heating capacity of
the heater
• Safety flame sensor at pilot burner
• Automatic overheating protection shut-off sensor
• Copper heating coils for endless supply of hot water
• Easily removable one-piece cover
• Easy one person installation
• Electronic Pilot Ignition driven by hydro-generator.
2.2 GWH-425-HNO specifications
(Technical data)
Approved in US/Canada
Capacity
Maximum flow rate: 3.7 GPM (14 l/min) at a 45°F
(25°C) rise.
Maximum output
101,772 Btu/h (29.8 kW)
Maximum input
117,000 Btu/h (34.3 kW)
Efficiency in %
Recovery efficiency 80%
Min. Output
28,000 Btu/h (8.2 kW)
Gas Requirement
Gas connection (inches) - ¾”
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 3.6.
Water
• Hot water connection (inches) - ½”
• Cold water connection (inches) - ½”
• 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
Dimensions
• Depth (in): 10.5” (265 mm)
• Width (in): 18.25” (460 mm)
• Height (in): 36.75” (936 mm)
• Weight: 64 pounds (29 kg).
Gas types
Natural Gas.
LP Gas
Safety devices
• Flame failure device (ionization flame rod sensor)
• Pressure relief valve (supplied with heater)
• Over heat prevention (temperature limiter).
Water resistant
IP X5 (protection against water drops).
i
BOSCH is constantly improving its
products, therefore specifications are
subject to change without prior notice.
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Appliance details
5
2.3 Unpacking the GWH-425-HNO
heater
This heater is packed securely.
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.
The box includes:
• Pressure relief valve
• Heat shield
• Mounting screws
• Product registration card
• Installation manual.
Do not lose this manual, there is a charge for a
replacement.
Please complete and return the enclosed product
registration card.
The GWH-425-HNO is not approved or designed
for:
• Manufactured (mobile) homes, RV's or boats
• Heating or other recirculating/pumping applications*
• Solar/preheat backup or high temperature booster
use
* This includes domestic hot water circulator pump loop
systems that may previously exist in a home hot water
system. The use of a small electric mini-tank (4-6 gallon
size) should be used for this application; when
designed so the pump will circulate the hot water in the
mini-tank only and through the building's hot water
return loop (timed or thermostatic controlled operation
of the pump is commonly done). The GWH-425-HNO
should be plumbed in line before the mini-tank water
heater, contact BBTNA if further instruction is needed.
2.4 General rules to follow for safe
operation
B 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.
In Canada: The Installation should conform with
CGA B149.(1,2) INSTALLATION CODES and /or
local installation codes.
B 2. Carefully plan where you install the heater. Proper
clearances must be followed.
B 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.
B 4. Keep water heater area clear and free from
combustibles and flammable liquids. Do not locate
the heater over any material which might burn.
B 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 section on connecting the gas supply.
B 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.
B 7. Do not use this appliance if any part has been
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.
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Appliance details
2.5 Dimensions and installation clearances
Fig. 3 Dimensions
Fig. 4 Minimum clearances
Model GWH-425-HNO
TOP (A) 3 ft.
FRONT (B) 4 ft.
BACK 0”
SIDES 4 ft.
BOTTOM (C) 1 ft.
Table 1 Minimum clearances
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Installation instructions
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3 Installation instructions
3.1 Introduction
Please follow these instructions. Failure to follow
instructions may result in:
B Damage or injury.
B Improper operation.
B Loss of warranty.
Please contact BBT North America with any questions.
3.2 Proper location for installing your
heater
Carefully select the location of the water heater.
Follow the guidelines below:
B 1. Locate the heater where an adequate gas line size
and 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 to
prevent the possibility of any freeze damage.
B 3. The water in this heater is cold and always remains
cold except for the times that hot water is being used.
The heater is equipped with freeze prevention
equipment that will operate and prevent freezing of
the water in the heater to 5°F with no wind chill.
Electrical power must be maintained to the heater to
allow this to function.
WARNING: Proper insulation of the
water lines below the heater is required
if below freezing temperatures, below
32°F, are ever anticipated!
Danger: If the temperature drops
below 32°F, freeze damage to the water
heater itself must be prevented by
turning off the power to the heater, then
disconnecting the plumbing connections, as well as removing the drain
plug and introducing short bursts of
compressed air (20-40 psi) through the
heater's connections. This will remove
the residual water in the horizontal
pipes and water valve.
Danger: Keep children away as the top
of the water heater vent cap will get very
hot during operation. Install in a place
that prevents the top of the heater being
reached by small children.
Danger: Flue gases will be released
through the vent cap. Flue gas is very
hot and contains carbon monoxide. The
heater cannot be installed indoors. To
prevent risk of fire and poisoning by
carbon monoxide, assure all clearances
indicated in manual.
Danger: Surface temperature around
vent cap is less than 140°F, except
highest top surface of vent cap may
reach 300°F.
Danger: Do not place or store any
combustible material within 5 feet of the
appliance. Risk of fire could be caused
by hot flue gas.
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
3.3 Heater placement and clearances
The GWH-425-HNO is design certified for installation
directly on a combustible wall. (see 3.4 Mounting
installation) For installation on vinyl siding see Fig. 7.
Keep the area below the heater free of combustible
material.
Minimum clearances
If the appliance is installed under an overhang, there
must be a 36” clearance from the top of the appliance
and the mounting area must be open in front and on the
sides of the appliance.
Fig. 5
3.4 Mounting installation
To remove front cover.
B Loosen the two screws located on the sides of the
front panel, see Fig. 6.
Fig. 6 Remove front cover
B Ensure that the flue terminal is clear of any
combustible material.
B After inspection, replace front cover and tighten
screws.
B Install only on an external wall, as close as possible
to the most frequently used hot tap (note clearances
in chapter 3.3.
B If the unit is to be installed on a combustible surface
use the enclosed heat shield (see Fig. 5).
Danger: The top of the kit will get hot
due to the flue gases. Install away from
children.
Ref. Description
Min.
distances
A Directly below or from an
opening; operable windows,
doors and any fresh air
openings
≥ 4 ft
B
C
D
From any adjacent wall or tall
shruberry
≥ 4 ft
E
Below a gutter, sanitary
pipework, eaves or overhang
≥ 3 ft
F Above ground ≥ 1 ft
G
From a gas meter, gas
regulator, electrical box or
another 425-HNO heater.
≥ 3 ft
Table 2 Clearances
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.
i
Front cover should be removed in order to
inspect components visually (see
instructions below).
Warning: Do not mount heater directly
to vinyl siding. With vinyl siding
surfacing, a 6' x 4' area of the siding
must first be covered or replaced with
wood or other non-plastic made
material. See Fig. 7.
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