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Bosch GWH C 920 ES Instruction Manual

Indoor residential and commercial models temperature modulated with electronic ignition suitable for heating potable water - not approved for space heating purposes (intended for variable flow applications)
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GWH C 920 ES/ESC
INDOOR RESIDENTIAL AND COMMERCIAL MODELS
Temperature Modulated with Electronic Ignition
Suitable for heating potable water - Not approved for space heating purposes
(Intended for variable flow applications)
GWH C 920 ES/ESC - Natural Gas
GWH C 920 ES/ESC - Liquefied Petroleum (LP) Gas
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
vapors and liquids in the vicinity of this or any other
appliance.
Improper
installation,
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 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.
adjustment,
alteration,
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.
• 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.

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Summary of Contents for Bosch GWH C 920 ES

  • Page 1 Suitable for heating potable water - Not approved for space heating purposes (Intended for variable flow applications) GWH C 920 ES/ESC - Natural Gas GWH C 920 ES/ESC - Liquefied Petroleum (LP) Gas Warning: If the information in this manual is not What to do if you smell gas followed exactly, a fire or explosion may result •...
  • Page 2 Annual maintenance Winterizing for seasonal use Appliance details Mineral scale build-up Features Condensing heat exchanger unit GWH C 920 ES and GWH C 920 ESC Adjusting CO2 Specifications (Technical data) Program values Unpacking the tankless water heater Control unit diagnostics...
  • Page 3 Warning: heater must may be needed to improve performance. disconnected from the gas supply Contact Bosch Water Heating for piping system during any pressure additional information. testing of that system at test pressures equal to or more than 0.5 psig.

  • Page 4: Appliance Details

    Residential/commercial models Warning: When manually operating the relief valve, precautions must be taken • GWH C 920 ES residential model prior to operating the relief valve to avoid – maximum temperature 140° F contact with hot water coming out of the •...

  • Page 5: Specifications (Technical Data)

    Appliance details GWH C 920 ES and GWH C 920 ESC • CO ≤ 290 ppm (measured) Specifications (Technical data) • CO level set from factory, see chapter 6.5, page 37. Approved in US/Canada Dimensions • Depth (in): 11¼" (286 mm) Capacity •...
  • Page 6 Appliance details Unpacking the tankless water To remove front cover heater B Loosen the two Philips head screws located on bottom rear of cover (see Fig. 3). Before installing the unit, be certain you have the correct heater for your type of Gas - Propane or Natural Gas.

  • Page 7: General Rules To Follow For Safe Operation

    Appliance details General rules to follow for safe B 10. Failure to install heater correctly may lead to unsafe operation and void the warranty. operation B 11. Water temperatures over 125°F can cause B 1. You must follow these instructions when you severe burns instantly.
  • Page 8 Appliance details Dimensions and minimum installation clearances 6720608000-03.2AL Fig. 6 Dimensions On/Off button Model GWH C 920 ES Reset button Program button " TOP (A) Power ON or stand-by LED LCD display " FRONT (B) Up button " BACK Down button "...

  • Page 9: Installation Instructions

    Concentric termination or hazardous condition such as explosion or separate terminations for combustion carbon monoxide poisoning could result. and vent, must be installed on the same Bosch Thermotechnology Corp. is not wall or roof surface; however, never responsible improperly installed facing the direction of prevailing winds.
  • Page 10 Installation instructions 3.3.1 Vent material All combustion air and vent pipe materials and fittings must comply with the following: EXHAUST MAINTAIN 12 IN. (18 IN. FOR CANADA) MINIMUM CLEARANCE ABOVE Item Material United States Canada HIGHEST ANTICIPATED SNOW LEVEL. MAXIMUM OF 24 IN. ABOVE ROOF. COMBUSTION ROOF BOOT/ PVC schedule 40...
  • Page 11 Installation instructions 3.3.2 Vent specifications Step 1: If using the twin pipe penetration system, refer to table 5. If using the concentric vent kit Establish vent clearances that comply with the vent system, refer to table 6. manufacturer's specifications applicable national/local codes.
  • Page 12 Installation instructions Required direct vent terminal clearances (twin pipe / concentric penetration) 6720608836-23.1Av Fig. 9 Canadian installations U.S. installations Clearance above grade, veranda, porch, deck or balcony 12 in. 12 in. Clearance to window or door that may be opened 36 in.
  • Page 13 Installation instructions Required other than direct vent terminal clearances (single pipe penetration) 6720608836-23.1Av Fig. 10 Canadian installations U.S. installations Clearance above grade, veranda, porch, deck or balcony 12 in. 12 in. Clearance to window or door that may be opened 36 in.
  • Page 14 Installation instructions 3.3.3 Vent configuration examples Below are approved examples of vertical and horizontal venting installations. MAINTAIN 12 IN. (18 IN. FOR CANADA) MINIMUM CLEARANCE ABOVE HIGHEST ANTICIPATED SNOW LEVEL. MAXIMUM OF 24 IN. ABOVE ROOF. EXHAUST 6720608836-25.1Av Fig. 13 Horizontal parallel venting system (twin pipe INTAKE direct vent) DRAIN TEE...
  • Page 15 Installation instructions 3.3.4 Vent connections 3.3.5 Connecting the condensate water drain Warning: Attaching the exhaust and air inlet connection adaptors to the top of the heater B Failure to properly install condensate drain can damage the appliance and will B Attach the flue gas exhaust accessory to the top of void the warranty.
  • Page 16 Installation instructions External condensate drain installation 3.3.6 Fan speed adjustment If an external condensate drain (installer supplied) must ! IMPORTANT INFORMATION: be installed (Section 3.3.2), the following Natural gas heaters with installation altitudes recommended: below 2,000 ft above sea level disregard this section.
  • Page 17 Installation instructions Summary Exhaust Exhaust Straight section length __ = ____ Straight section length (feet) 11 x 1 = 90° elbows (qty) __ x 5 = ____ 90° elbows (qty) 0 x 5 = 45° elbows (qty) __ x 3 = ____ Total: ____...
  • Page 18 Installation instructions NG/LPG Altitude Minimum Minimum Maximum Vent Total equivalent (above sea power fan power fan power fan terminal vent length level) speed (P2) speed (P2) speed (P1) 8 - 25 ft Concentric 26 - 46 ft 0 - 2000 ft (0 - 610 m) 8 - 37 ft For operation at...
  • Page 19 Installation instructions Attention residents of the Commonwealth of Massachusetts: In the Commonwealth of Massachusetts the following signage installed in accordance with the provisions of regulation went into effect on 12/30/2005: 248 CMR 5.08(2)(a)1 through 4. (a)For all side wall horizontally vented gas fueled (b)EXEMPTIONS: The following equipment is exempt equipment installed in every dwelling, building or from 248 CMR 5.08(2)(a)1 through 4:...

  • Page 20: Combustion Air Requirements

    That would be 11250 cubic feet (318.6 freezing, sealed combustion operation cubic meters) for the GWH C 920 ES alone. required. concentric – b) In unconfined spaces in buildings of...

  • Page 21: Proper Location For Installing Your Heater

    Installation instructions Proper location for installing your Mounting installation heater Warning: before starting installa- Carefully select the location of the water heater. For tion: safety and for proper heater operation, you must provide B Check that there are no loose or combustion air to the heater and a proper exhaust vent damaged parts inside the appli- system.

  • Page 22: Gas Piping & Connections

    Installation instructions Gas piping & connections 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.
  • Page 23 Installation instructions Minimum Gas supply 3” Inlet gas particle screen (included) Fig. 23 Gas connection Gas piping Once connections are made, check for gas leaks at all joints. Apply some gas leak detection solution to all gas Fig. 24 fittings. Bubbles are a sign of a leak. A combustible gas detector may also be used to detect for leaks.
  • Page 24 0.3” in Water Column (0.75mbar).(Based on a 0.60 Specific Gravity Gas) Btu numbers given in thousands. Follow boxed numbers for piping just one GWH C 920 ES/ESC (example: ¾” B.I. Natural Gas pipe for 10 ft (3.0m). will handle 278,000 btu’s (81.5 kWh). For multiple appliances combine the total maximum btu input load and then refer to applicable chart below.

  • Page 25: Water Connections

    Installation instructions Water connections B Never sweat any piping directly to or beneath the water connections, as damage will occur to the internal water valve from heating of the Warning: This heater is not approved pipe. for preheated water supply exceeding 140°F (60°C).

  • Page 26: Water Quality

    4" above a drain and installed such that it specified below, Bosch recommends installing a water allows complete drainage of both the PRV and the line. conditioner or softener. If the tankless water heater is...

  • Page 27: Domestic Hot Water Recirculation

    Timed or thermostatically controlled operation of the pump is commonly done. Contact Bosch Water Heating if further information is needed. 6 720 608 836...

  • Page 28: Filling The Condensate Trap

    Installation instructions 3.12 Filling the condensate trap B Fill the condensate trap by pouring approximately 14 oz. (400ml) of water into the top of the drain tube. To The condensate trap can be filled before or after avoid damage to the appliance use a funnel in this connecting the vent pipe.

  • Page 29: Measuring Gas Pressure

    Installation instructions 3.13 Measuring gas pressure possible error code faults and must be corrected. See Gas Connections, chapter 3.8, page 22. Gas pressure must be measured upon installation. P1 fan speed: Factory default: NG: 52, LP: 53 Connecting manometer Lowering P1 fan speed reduces the maximum BTU B Shut off gas supply at installer supplied shutoff valve input.

  • Page 30: Electrical Connections

    Electrical connections Electrical connections Electrical power supply Position of the fuses in control unit To check fuses, proceed as follows: safety reasons, Warning: B Unplug the water heater's power cord. disconnect the power supply cord to the heater before any service or testing B Remove the front cover, see Fig.

  • Page 31: Description Of Lcd Display

    Operation instructions Operation instructions Fig. 40 On/Off button Reset button Program button LCD display Up button Down button Power On or stand-by LED Description of LCD Display Fig. 44 Locked condition indicator (only with remote Warning: Do not use any cleaning control) agressive or corrosive agents to clean the window.

  • Page 32: Temperature Selection

    Operation instructions For your safety read before Temperature selection operating your water heater To select hot water temperature: B Press buttons in order to reach desired Warning: If you do not follow these temperature. instructions exactly, a fire or explosion may result causing property damage, personal injury or loss of life.

  • Page 33: Operation

    Operation instructions Solar mode Operation The water heater will not ignite if inlet water temperature B When a hot water tap is opened, main burner ignites exceeds the set temperature on the appliance. In this and LCD displays indication condition, the solar mode indicator will show on the LCD display.

  • Page 34: Maintenance And Service

    Maintenance and service 5.8.1 Memorizing selected temperature Maintenance and service B Press buttons to select desired Warning: Always shut off the electrical temperature. power supply, shut off the manual gas B Hold “Program” button for 3 seconds to save valve and shut off the water valves when temperature.

  • Page 35: Mineral Scale Build-Up

    Maintenance and service Inlet Water Filter water heater to catch residual water remaining inside the water heater. • Verify the inlet filter screen is clean and undamaged. 6. Using an air compressor, blow short bursts of air The inlet water filter is located between the ¾" cold (100psi max) through the outlet water connection water inlet fitting on the right side of the appliance, until there is no water present coming through the...
  • Page 36 If replace the gaskets and o-rings. repairs are needed, the repairs should be done by a cer- tified Bosch technician. B Assemble the condensate unit and all other parts in reverse order of disassembly.
  • Page 37 Maintenance and service P1 Operating Pressure: “ WC B Record the CO reading in P2 below. P1 CO Reading: % CO The P1 minimum operating gas pressure is 3.5" WC for Natural Gas and 8" WC for Propane. Do not proceed in P2 CO Reading: % CO...
  • Page 38 Maintenance and service Final Readings P1 CO Reading: % CO P2 CO Reading: % CO D. Returning to Service: 1. Return slotted screw cover to original position. 2. Reinstall Torx cover. 3. Remove CO analyzer probe and reinstall flathead screw with gasket in exhaust collar. 4.

  • Page 39: Program Values

    Program Description Factory Default Comment Temperature range This values are set from factory H: GWH C 920 ES settings they cannot be changed. C: GWH C 920 ESC Maximum Fan NG:52, LP:53 NG:52, LP:53 see chapter 3.13, page 29...

  • Page 40: Control Unit Diagnostics

    Maintenance and service Control unit diagnostics Diagnostic menu 1. Press ON/OFF button to turn off the appliance. Entry/Exit into sub-modes 2. Press and hold "Program" button and press Set-point temperature ON/OFF button to turn appliance ON. Inlet water temperature (°F) 3.

  • Page 41: Troubleshooting

    Troubleshooting Troubleshooting single lever faucet mixing valves are common causes Warning: If you are unable to perform of plumbing crossovers. the tasks listed below, or need 8. With the power button pressed to OFF and the additional assistance please contact power supply cord unplugged, remove the unit's your original installer or a licensed gas front cover (See Page 6.

  • Page 42: Low Water Flow/Pressure

    Troubleshooting Contact your original installer or a local certified gas coming outlet. Consult technician to obtain this reading. www.boschpro.com for a detailed service bulletin on overcoming temperature fluctuations. 7. Cold water is mixing into the hot water lines (plumbing crossover). A plumbing crossover can 2.
  • Page 43 Troubleshooting specifications in Section 3.4, page 20 Combustion Air Requirements. 4. Cross contamination. Ensure that intake and exhaust terminations maintain required clearances as stated in chapter 3.3, page 9. Cross contamination between intake and exhaust may cause unstable burner flames and noise. 5.

  • Page 44: Error Code Diagnostics

    3. Check gas pressure. Low gas pressure may prevent the heater from reaching desired output temperature. 4. Check supply voltage. It must be 120VAC and properly grounded. 5. Possible defective control unit, call Bosch Water Heating for further instructions. Table 20 6 720 608 836...
  • Page 45 5. Check gas pressure. Low gas pressure may cause the fan to change its speed to meet desired temperature. 6. Possible defective control unit call Bosch Water Heating for further instructions. No rotational speed sensor signal 1.
  • Page 46 3.3 page 9 venting may cause this failure. See 4. Call Bosch Water Heating for further instructions. Overheat sensor (ECO) open 1. Disconnect power supply cord and check wire connections on Fig. 69...
  • Page 47 3. Gas valve may be defective, contact Bosch Water Heating for further instrucation. Table 20 6 720 608 836...

  • Page 48: Electrical Diagram

    Electrical diagram Electrical diagram T=90°C T=194°F T=104°C T=220°F T=110°C T=230°F Casc. input Casc. output Back flow 6720608158-01.1AL Fig. 64 Electrical scheme Inlet water temperature sensor Outlet water temperature sensor Backflow temperature sensor Cascading output connection Cascading input connection Ionization sensor Water flow sensor Flue gas limiter Heat exchanger overheat sensor (ECO)

  • Page 49: Sensor Resistance Charts

    Sensor resistance charts Sensor resistance charts Outlet sensor characteristics 2 2 2 2 17 10 5 2 12 10 0 2 0 7 2 0 2 19 7 19 2 18 7 18 2 16 7 16 2 14 7 14 2 13 7 13 2...
  • Page 50 Sensor resistance charts Back Flow and Exhaust sensor characteristics 3 0 2 2 9 7 2 9 2 14 5 2 8 7 2 8 2 14 0 2 7 7 2 7 2 13 5 2 6 7 2 6 2 13 0 2 5 7 12 5...

  • Page 51: Functional Scheme

    Functional scheme Functional scheme Fig. 68 Functional scheme 6 720 608 836...

  • Page 52: Interior Components

    Interior components diagram and parts list Interior components diagram and parts list 12.1 Interior components 6720608836-06.1AL Fig. 69 Components Exhaust temperature sensor Observation window Condensing heat exchanger Backflow temperature sensor Heat exchanger Secondary air fan Ionization sensor Gas valve Primary fan (Mixer) Condensate trap LCD display Control unit...
  • Page 53 Interior components diagram and parts list 6720608836-02.1AL Fig. 70 Appliance overview 6 720 608 836...

  • Page 54: Components Diagram

    Interior components diagram and parts list 12.2 Components diagram 12.2.1 Group 1 13 15 6720902973.AB JF Fig. 71 Components Diagram Item Description Reference Item Description Reference Combustion cover clip 8 701 201 032 Front cover 8 705 431 264 Grommet set 8 710 203 039 Cover shield 8 705 506 857...
  • Page 55 Interior components diagram and parts list 12.2.2 Group 2 6720902987.AA JF Fig. 72 Components Diagram 6 720 608 836...
  • Page 56 Interior components diagram and parts list Item Description Reference Heat exchanger 8 705 406 419 Heat exchanger top gasket 8 704 701 052 Condensing exchanger inlet 8 705 700 159 Overheat sensor (ECO) 8 707 206 204 Heat exchanger bottom gasket 8 704 701 054 Site window 8 701 000 401...
  • Page 57 Interior components diagram and parts list 12.2.3 Group 3 6720902988.AA JF Fig. 73 Components Diagram Item Description Reference Item Description Reference Gas / Air Mixer 8 705 700 170 Main burner - NG 8 708 120 650 Venturi 8 700 306 226 Main burner - LPG 8 708 120 673 O-ring...
  • Page 58 Interior components diagram and parts list 12.2.4 Group 4 6720902990.AA JF Fig. 74 Components Diagram Item Description Reference Item Description Reference Gas filter 8 700 507 002 Gas valve 8 707 021 019 Gasket 8 704 701 107 Pressure tapping 8 703 404 219 Gas / Fan connector 8 705 202 140...
  • Page 59 Interior components diagram and parts list 12.2.5 Group 5 (optional) 6720902989.AA JF Fig. 75 Components Diagram Item Description Reference Item Description Reference Inlet fitting 8 703 305 348 Water valve with engine and 8 708 505 024 temperature sensor O-ring 8 700 205 157 O-ring 8 700 205 147...
  • Page 60 Reference Item Description Reference Jumper 8 704 401 376 Control unit - GWH C 920 ES 8 707 207 305 Electrode cables 8 704 401 346 Control unit - GWH C 920 ESC 8 707 207 348 Flue gas limiter 8 700 400 032 Fuse T2.5A...

  • Page 61: Protecting The Environment

    Protecting the environment 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.

  • Page 62: Limited Warranty

    Limited Warranty Limited Warranty 14.1 Limited warranty for GWH C 920 ES Service Labor Costs residential model This warranty does not cover any labor costs associated with service, removal or re-installation of General part(s). All such costs must be borne by the Purchaser.
  • Page 63 This warranty does not cover any labor costs associated with service, removal or re-installation of General part(s). All such costs must be borne by the Purchaser. BOSCH tankless water heaters are warranted by the Additionally, this warranty does not cover any labor Manufacturer (BOSCH)
  • Page 64 Installation manual should be left with the owner after the installation is tested and completed BOSCH THERMOTECHNOLOGY CORP. Bosch Termotecnologia SA 50 Wentworth Avenue Estrada de Cacia Londonderry, NH 03053 Tel. 866-330-2730 3801 - 856 Aveiro - PORTUGAL www.boschpro.com Recycled paper © 2009 Bosch Thermotechnology Corp., Londonderry, NH...

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