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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 What to do if you smell gas
followed exactly, a fire or explosion may result
Close gas valve. Open windows.
causing property damage, personal injury or death.
Do not try to light any appliance
Do
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Index Index 1 Warning 1 Warning 2 2 Appliance details 3 2.1 GWH 425 PN specifications (Technical data) 3 Warning: The heater must be isolated 2.2 Unpacking the GWH 425 PN heater 4 from the gas supply piping system 2.3 General rules to follow for safe operation 4 during any pressure testing of that 2.4 Dimensions and installation clearances 5 system at test pressures equal to or more than 0.5 psig. 3 Installation instructions 6 3.1 Introduction 6 3.2 Proper location for installing your heater 6 C
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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) Approved in US/Canada Width (in): 18.11 (460 mm) Capacity Height (in): 25.79 (655 mm) GWH 425 PN: 4.3 GPM Weight: 35 pounds (16 kg). Maximum output Gas types GWH 425 PN: 91 525 Btu/hr Natural Gas. Maximum input LP Gas GWH 425 PN: 117 000 Btu/hr Safety devices Efficiency in % Flame failure device (ionization flame rod sensor) Recovery efficiency 78%
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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 Before installing the unit, be certain you have the your heater. In the United States: The installation must correct heater for your type of Gas - Propane or conform with local codes or, in the absence of local Natural Gas. Identification labels are found on the codes, the National Fuel Gas Code ANSI Z223.1/
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Appliance details 2.4 Dimensions and installation clearances Fig. 3 Dimensions in Inches and (mm) 4 Heat exchanger 5 Burner Dimensions inches 10 Temperature control (mm) 11 Water valve 20 Gas connection GWH 425 PN 26 Output control 36 Front cover A 16.73 (425) 37 Hole for fixing to wall 38 Exhaust pipe to wall B 25.75 (655) 39 Draught diverter with flue gas monitor C 13.15 (334) 40 Gas valve 49 Observation window D 5.11 (130) 102 Piezo E 21.25 (540) F 2.55 (65) G 1.18 (30) H 3/4 Table 1
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Installation instructions 3 Installation instructions 3.1 Introduction Warning: The heater must be isolated from the gas supply piping system Please follow these instructions. Failure to follow during any pressure testing of that instructions may result in: system at test pressures equal to or B Damage or injury. more than 0.5 psig. B Improper operation. B Loss of warranty. Warning: Place the heater in a location If you are unable to perform the tasks required to install where water leaks will d
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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 i Fig. 6 Remove front cover instructions below). Remo
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Installation instructions Fuel Gas Code for complete information. In buildings of 3.5 Combustion air requirements tight construction all air should be taken from outside. 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
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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 Any gas vent section that is greater than 45 degrees of heater. Failure to follow venting from the vertical is considered horizontal. Horizontal requirements may cause dangerous sections must slope upwards at least ¼ inch for every exhaust gases to enter living
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Installation instructions Masonry chimney LOWEST DISCHARGE LISTED VENT CAP Masonry chimneys shall be built and installed in OPENING accordance with NFPS 211 or local codes. A minimum 5" diameter gas vent pipe (metal double wall Type B), H (minimum) height or an approved clay flue liner or a listed chimney lining from roof to lowest X discharge opening system must be used when venting into a naturally 12 drafting, internal masonry chimney. 6 inch is required in ROOF MINIMUM 6 elevations great
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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 connector used is ¾. plate on the right side of the heater to be sure that the B National Fuel Gas Code requires that a sediment heater is rated for the same gas to which it will be trap (drip leg) be installed on gas appliances not so connected. equipped. The drip leg must be accessib
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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
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Installation instructions Although water piping throughout your structure may be 3.8 Measuring gas pressure other than copper, we recommend that copper piping Connecting manometer or suitably rated stainless steel flex line piping be used for at least three feet before and after the heater (follow B Shut off gas. local codes if more stringent). Never sweat any rigid B Remove front cover and locate inlet gas pressure piping directly to or beneath the water connections, measuring point on the righ
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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 4.1 For your safety read before a proper recirculation application using the BOSCH operating your water heater PRO water heater with an Ariston minitank. This schematic is for illustration only and must not be used Warning: If you do not follow these for actual installation without appropriate engineering instructi
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Operation instructions B With the gas valve button fully depressed, light pilot 4.2 Lighting instructions by pushing the piezo button. This step may have to B STOP! Read the previous safety information. be repeated. 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 B Observe the pilot flame through the peephole. The gas, STOP! Follow B in chapter 4.1. If you dont gas valve
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Operation instructions The hottest position is the highest flame position all the 4.4 Setting the water temperature way to the right. 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
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Maintenance and service 5 Maintenance and service clip on water valve assembly and pulling the pipe free 5.1 Maintenance intervals from the water valve. Loosen the two set screws at the bottom of the water valve where it connects to the gas Warning: Failure to perform valve. If the set screws are seized, STOP and call recommended maintenance may result Bosch tech support before proceeding. Forcing and in complete failure of the unit over time. snapping seized set screws may cause irrevocable Th
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Maintenance and service 12. Run solution through the heat exchanger until the 5.4 Main burners solution returning to the descaling reservoir comes out The main burner flames should be blue, with a more clear. (Changing to a fresh solution may be necessary intense blue cone in the center core. Yellow flames during this process). could be a sign of wrong size gas orifices or dirty 13. Disconnect all lines and drain all solution from heat burners, a blockage on the heat exchangers fins. If exchange
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Troubleshooting 6 Troubleshooting electromagnet (See parts diagram for locations). Clean 6.1 Introduction sensor connections with light sandpaper if corrosion is Many of the questions customers ask regarding evident. The electromagnet connection is 5mm nut from operation of this unit can be answered by following the the thermocouple which screws into a larger 17mm nut. troubleshooting steps as outlined below. Visit our web Tighten both nuts snugly but do not over tighten. site at www.boschpro.co
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Troubleshooting 6. Verify pilot flame completely engulfs the 2. Check for a clogged inlet water filter screen (see thermocouple tip. If pilot is too small, clean pilot orifice chapter 5.2). (see chapter 5.3). 3. Hot water is very hot out of the tap, requiring a lot of 7. If the water has a high mineral content, the heat cold water to be added with it in order to attain a exchanger may be scaled internally. This restricts the useable hot water temperature. The addition of too water path, causi
