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 6 720 608 836 (2008/12) US Warning: If the information in this manual is not followed exactly, a fire or explosion may result causing property damage, personal injury or death.
Index Index 1 Warning 3 2 2.1 2.
Warning 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: Carefully plan where to install the heater. Correct combustion air supply and flue pipe installation are very important. If a gas appliance is not installed correctly, fatal accidents can result such as carbon monoxide poisoning or fire.
Appliance details Warning: Do not obstruct the flow of combustion and ventilation air. Warning: When manually operating the relief valve, precautions must be taken prior to operating the relief valve to avoid contact with hot water coming out of the relief valve and to prevent water damage. 2 Appliance details 2.
Appliance details 2.2 GWH C 920 ES and GWH C 920 ESC Specifications (Technical data) • CO ≤ 290 ppm (measured) • CO2 level set from factory, see chapter 6.5, page 37. Approved in US/Canada Dimensions Capacity • Depth (in): 11¼" (286 mm) Maximum flow rate: 9.2 GPM (35 l/min) at a 45°F (25°C) rise. (with sufficient water pressure) • Width (in): 17 7/8" (452 mm) • Height (in): 30½" (775 mm) Maximum output • Weight: 88 pounds (40 kg). 210,000 Btu/h (61.
Appliance details 2.3 Unpacking the tankless water heater 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. To remove front cover B Loosen the two Philips head screws located on bottom rear of cover (see Fig. 3). Fig. 3 Loosen the two screws B Lift front cover upward and remove. Fig.
Appliance details 2.4 General rules to follow for safe operation B 1. You must 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 must conform with CSA B149.(1,2) INSTALLATION CODES and /or local installation codes. B 10. Failure to install heater correctly may lead to unsafe operation and void the warranty. B 11.
Appliance details 2.5 Dimensions and minimum installation clearances Fig. 6 Dimensions 1 2 3 4 5 6 7 On/Off button Reset button Program button Power ON or stand-by LED LCD display Up button Down button Model GWH C 920 ES TOP (A) 12" FRONT (B) 1" BACK 0" SIDES 1" FLOOR (C) 12" Table 1 Minimum clearances Fig. 7 Minimum clearances Note: For servicing access, a 2 foot clearance is recommended to the front cover.
Installation instructions 3 Installation instructions 3.1 Specialized tools 3.3 Venting The following specialized tools may be required for installation: Warning: • Manometer B Do not reduce the exhaust combustion air vent pipe sizes. • Multi-meter or • Combustion Gas Analyzer. B Do not common vent with any other vented appliance or stove. 3.2 B Do not use Type-B vent as the actual exhuast vent system for the appliance. Introduction Please follow these instructions.
Installation instructions 3.3.1 Vent material All combustion air and vent pipe materials and fittings must comply with the following: Item Vent or air pipe and fitting Material United States PVC schedule 40 ANSI/ASTM D1785 PVC-DWV ANSI/ASTM D2665 CPVC schedule 40 ANSI/ASTM F441 ABS-DWV schedule 40 ANSI/ASTM D2661 PVC Pipe cement / CPVC primer ABS Canada MAINTAIN 12 IN. (18 IN. FOR CANADA) MINIMUM CLEARANCE ABOVE HIGHEST ANTICIPATED SNOW LEVEL. MAXIMUM OF 24 IN. ABOVE ROOF.
Installation instructions 3.3.2 Vent specifications Establish vent clearances that comply with the vent manufacturer's specifications and all applicable national/local codes. Venting specifications Diam. Aproved terminals “T” terminal E x h a u s t 90° elbow 3 or 4 inches Concentric (BWH60L46) Step 1: If using the twin pipe penetration system, refer to table 5. If using the concentric vent kit system, refer to table 6. Step 2: Total the number of 90° elbows and 45° elbows used on the exhaust piping.
Installation instructions Required direct vent terminal clearances (twin pipe / concentric penetration) 6720608836-23.1Av Fig. 9 Canadian installations1) U.S. installations2) A Clearance above grade, veranda, porch, deck or balcony 12 in. 12 in. B Clearance to window or door that may be opened 36 in. 12 in.
Installation instructions Required other than direct vent terminal clearances (single pipe penetration) 6720608836-23.1Av Fig. 10 Canadian installations1) U.S. installations2) A Clearance above grade, veranda, porch, deck or balcony 12 in. 12 in. B Clearance to window or door that may be opened 36 in.
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 3" (80mm) 6720608836-25.1Av Fig. 13 Horizontal parallel venting system (twin pipe direct vent) INTAKE DRAIN TEE EXHAUST INTAKE 4” Min. DRAIN TEE 6720608836-24.1Av Fig.
Installation instructions 3.3.4 Vent connections 3.3.5 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 void the warranty. B Attach the flue gas exhaust accessory to the top of the unit Fig. 13 (position 1) using the 4 screws and gasket provided, and fully insert vent pipe into the accessory.
Installation instructions External condensate drain installation 3.3.6 If an external condensate drain (installer supplied) must be installed (Section 3.3.2), the following is recommended: ! IMPORTANT INFORMATION: Natural gas heaters with installation altitudes below 2,000 ft above sea level disregard this section. • 1. Install condensate drain on a horizontal section of the exhaust pipe as close to the heater as possible. • 2. The condensate must be disposed of according to local codes. • 3.
Installation instructions Summary Exhaust 1 Straight section length 2 3 Exhaust __ = ____ 90° elbows (qty) __ x 5 = ____ Straight section length (feet) 11 x 1 = 11 45° elbows (qty) __ x 3 = ____ 90° elbows (qty) 0x5= 0 Total: ____ 45° elbows (qty) 0x3= 0 4 Intake 11 Total: 1 Straight section length __ x 1 = ____ 2 90° elbows (qty) __ x 5 = ____ 3 45° elbows (qty) __ x 3 = ____ 4 Total: ____ 5 Total equivalent vent length = ____ Table 10Determining vent length c
Installation instructions Altitude (above sea level) 0 - 2000 ft (0 - 610 m) 2000 - 4500 ft (610 - 1372 m) 4500 - 8000 ft (1372 - 2439 m) Table 12 1) Vent terminal Total equivalent vent length1) 8 - 25 ft Concentric 26 - 46 ft 8 - 37 ft Twin system 38 - 62 ft 8 - 25 ft Concentric 26 - 46 ft 8 - 37 ft Twin system 38 - 62 ft 8 - 25 ft Concentric 26 - 46 ft 8 - 37 ft Twin system 38 - 62 ft NG LPG NG/LPG Minimum power fan speed (P2) 12 12 12 12 12 13 12 13 13 13 13 13 Minimum power fan sp
Installation instructions Attention residents of the Commonwealth of Massachusetts: In the Commonwealth of Massachusetts the following regulation went into effect on 12/30/2005: signage installed in accordance with the provisions of 248 CMR 5.08(2)(a)1 through 4.
Installation instructions 3.4 Combustion air requirements Warning: In areas where outside temperatures routinely come close to freezing, sealed combustion operation is required. Use a concentric termination or separate terminations for combustion and vent, which must be installed on the same wall or roof surface, however never facing the direction of prevailing winds. Failure to do so may result in heat exchanger freezing up and bursting. This failure is not covered under the manufacturer's warranty.
Installation instructions 3.5 Proper location for installing your heater 3.7 Warning: before starting installation: Carefully select the location of the water heater. For safety and for proper heater operation, you must provide combustion air to the heater and a proper exhaust vent system. Follow the guidelines below: B Check that there are no loose or damaged parts inside the appliance B Confirm that the gas type of the heater matches the gas supply you will be connecting to the heater, See Fig.
Installation instructions 3.8 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. In Canada: The Installation must conform to CGA B149 INSTALLATION CODES and/or local installation codes.
Installation instructions Minimum 3” Gas supply Cap Fig. 23 Gas connection Once 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. Inlet gas particle screen (included) Gas piping Fig. 24 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.
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. 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).
Installation instructions 3.9 Water connections Warning: This heater is not approved for preheated water supply exceeding 140°F (60°C). B When facing the heater, the ¾" cold connection is on the bottom right and the hot connection is on the bottom left. Centrally locating the water heater is recommended to keep hot water distribution times even throughout the structure.
Installation instructions 3.10 Water quality Connecting the pressure relief valve (PRV) Water quality can have an impact on appliance longevity and may void the manufacturer's warranty. For water analysis data call your local water department, or if on a well, have well water analyzed periodically. If water quality exceeds one or more of the values specified below, Bosch recommends installing a water conditioner or softener.
Installation instructions 3.11 Domestic hot water recirculation Although recirculation directly through the tankless water heater is allowed, temperature stability is improved by recirculating through a mini-tank as shown in Fig. 30. By using the design in Fig. 30, there is no recirculation of hot water through the tankless water heater and therefore, does not affect the heat exchanger warranty of 15 years.
Installation instructions 3.12 Filling the condensate trap The condensate trap can be filled before or after connecting the vent pipe. B Fill the condensate trap by pouring approximately 14 oz. (400ml) of water into the top of the drain tube. To avoid damage to the appliance use a funnel in this operation, see Fig. 32, page 28.
Installation instructions 3.13 Measuring gas pressure Gas pressure must be measured upon installation. Connecting manometer B Shut off gas supply at installer supplied shutoff valve for this water heater. B Remove front cover and locate inlet gas pressure test port (see Fig. 36). B Loosen screw inside left test point fitting (do not remove) and connect manometer tube to test point. possible error code faults and must be corrected. See Gas Connections, chapter 3.8, page 22.
Electrical connections 4 Electrical connections 4.1 Electrical power supply 4.2 Warning: For safety reasons, disconnect the power supply cord to the heater before any service or testing is performed. Warning: This heater must be electrically grounded in accordance with the most recent edition of the National Electrical Code. NFPA 70. In Canada, all electrical wiring to the heater must be in accordance with local codes and the Canadian Electrical Code, CSA C22.1 Part 1.
Operation instructions 5 Operation instructions Fig. 40 1 2 3 4 5 6 7 5.1 On/Off button Reset button Program button LCD display Up button Down button Power On or stand-by LED Description of LCD Display Warning: Do not use any cleaning agressive or corrosive agents to clean the window. Fig. 44 Locked condition indicator (only with remote control) Fig. 45 Flame indicator Fig. 41 Power bar indicator (input) Fig. 42 Temperature indicator Fig. 43 Error indicator 6 720 608 836 Fig.
Operation instructions 5.2 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. 5.4 Temperature selection To select hot water temperature: B Press buttons temperature. or in order to reach desired A. This appliance is equipped with electronic ignition for lighting the main burner. When turning the heater on, follow these instructions exactly.
Operation instructions Solar mode 5.6 Operation The water heater will not ignite if inlet water temperature exceeds the set temperature on the appliance. In this condition, the solar mode indicator will show on the LCD display. See Fig. 46, page 31. B When a hot water tap is opened, main burner ignites and LCD displays indication . DANGER Fig. 52 B LCD flashes until selected temperature is reached. HOT B Power bar indicates power percentage in use. 5.
Maintenance and service 5.8.1 Memorizing selected temperature B Press buttons temperature. or 6 Maintenance and service to select desired Warning: Always shut off the electrical power supply, shut off the manual gas valve and shut off the water valves when servicing. B Hold “Program” button for 3 seconds to save temperature. When LCD stops blinking, temperature is saved in memory.
Maintenance and service water heater to catch residual water remaining inside the water heater. Inlet Water Filter • Verify the inlet filter screen is clean and undamaged. The inlet water filter is located between the ¾" cold water inlet fitting on the right side of the appliance, and the water valve (See Fig. 27, page 25). Close installer supplied water shutoff, carefully lift the water valve, then rotate back. Remove filter, clean and or replace if damaged.
Maintenance and service 13. Disconnect all lines and drain all solution from heat exchanger. Properly discard of solution. B Remove the condensing heat exchanger unit from the appliance by pulling it towards you. 14. Position a container below the hot water outlet and connect cold water supply. Open cold water supply shutoff valve and flush heat exchanger with clean water. B Dismantle all parts for inspection and cleaning. 15.
Maintenance and service P1 Operating Pressure: “ WC The P1 minimum operating gas pressure is 3.5" WC for Natural Gas and 8" WC for Propane. Do not proceed in adjusting CO2 until pressure is at or above these levels, but not to exceed 10.5" WC for Natural Gas and 13" WC for Propane. B Record the CO2 reading in P2 below. P1 CO2 Reading: % CO2 P2 CO2 Reading: % CO2 Note: When making adjustments, combustion cover is installed. A.
Maintenance and service Final Readings P1 CO2 Reading: % CO2 P2 CO2 Reading: % CO2 D. Returning to Service: 1. Return slotted screw cover to original position. 2. Reinstall Torx cover. 3. Remove CO2 analyzer probe and reinstall flathead screw with gasket in exhaust collar. 4. Press ON/OFF button to turn OFF the heater and then turn ON the heater. 5. Heater is ready for normal operation. 1 3 2 6720608836-04.1AL Fig. 62 Adjusting P1 CO2 level 6720608836-05.1AL Fig.
Maintenance and service 6.6 Program values This section describes details on programming the appliance. For most applications the factory default values will provide robust and stable operation. Only adjust the factory settings if the installation requires changes as indicated in the appropriate section of this manual. Program Description P0 Factory Default Temperature range H: GWH C 920 ES settings Refer to chapter 6.7 Control board diagnostics (page 35) regarding how to access these P-modes.
Maintenance and service 6.7 Control unit diagnostics 1. Press ON/OFF button to turn off the appliance.
Troubleshooting 7 Troubleshooting Warning: If you are unable to perform the tasks listed below, or need additional assistance please contact your original installer or a licensed gas technician. 7.1 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 site at www.boschpro.com for more detailed troubleshooting. For best results, perform each step before proceeding to the next.
Troubleshooting Contact your original installer or a local certified gas technician to obtain this reading. 7. Cold water is mixing into the hot water lines (plumbing crossover). A plumbing crossover can unintentionally mix cold water with the hot water leaving the heater. The end result is a cooler water temperature than desired. To check for a plumbing crossover, shut off the cold water supply to the water heater. Then open all of the hot water taps served by the heater.
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. Lack of gas pressure. Inadequate gas pressure will cause the fuel-to-air mixture (CO2) to be out of adjustment. This will result in unstable burner flames and noise.
Error codes 8 Error codes 8.1 Error code diagnostics i To remove error code from the display, press the reset button. Display (Flashing) Cause Solution Fault in the flue gas limiter. Temperature above 230°F (110°C) inside the cabinet. 1. Check continuity of the flue gas limiter (see Fig. 69, page 52). Go to steps two and three to determine flue gas limiter fault and repair it. 2.
Error codes Display (Flashing) Cause Solution Primary fan rotation too low in operation. 1. Reset errors, disconnect power supply cord and check wire connection on back side of fan and the connectors on the control board, see Fig. 76, page 60. 2. Check supply voltage. It must be 120VAC and properly grounded. 3. Check that venting meets installation specifications. Long vent lengths, venting with more than three elbows, blocked vent or combination venting may cause this failure. 4.
Error codes Display Cause Solution Exhaust temperature sensor - the appliance will close the burner and lock if it gets over 194°F; (only applied for condensing unit). 1. Clean and check heat exchanger. 2. Clean and check condensing heat exchanger. 3. Reduce maximum power (chapter 3.13, page 29). 4. Reduce water temperature setting. Backflow temperature sensor over 309°F. The appliance will close the burner and lock (non-volatile). 1. Check inlet/outlet vent pipes. 2.
Error codes Display Cause Solution Ionization failure during operation. 1. Check gas type, Fig. 2, page 6. 2. Check three wire connections to ignition group on the lower front of the heat exchanger are secure. 3. Verify that venting specifications are met. Improper venting may cause premature failure of the flame sensor rod. See chapter 3.3, page 9. 4. Check gas pressure. See chapter 3.13, page 29. 5. Check and adjust CO2 readings. See chapter 6.5, page 36. 6.
Electrical diagram 9 Electrical diagram 16 20 15 13 M M 12 M E PS T=90°C T=194°F 11 10 19 T=104°C T=220°F 18 9 T=110°C T=230°F 8 FS 7 6 Casc. 5 input Casc. 4 output Back flow 3 2 1 17 16 ... 1 20 ... 1 21 14 JP2 JP7 JP5 JP8 JP6 22 6720608158-01.1AL Fig.
Sensor resistance charts 10 Sensor resistance charts 110 222 2 17 2 12 207 202 19 7 19 2 18 7 18 2 177 172 16 7 16 2 157 152 14 7 14 2 13 7 13 2 12 7 12 2 117 112 10 7 10 2 97 92 87 82 77 72 67 62 57 52 47 42 37 32 10 5 10 0 95 90 85 80 75 70 65 60 55 50 Temp ºC Temp ºF Outlet sensor characteristics 45 40 35 30 25 20 15 10 5 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 Resistance (kΩ) Fig.
Sensor resistance charts 155 302 297 292 287 282 277 272 267 262 257 252 247 242 237 232 227 222 2 17 2 12 207 202 19 7 19 2 18 7 18 2 17 7 17 2 16 7 16 2 15 7 15 2 14 7 14 2 13 7 13 2 12 7 12 2 117 112 10 7 10 2 97 92 87 82 77 72 67 62 57 52 47 42 37 32 150 14 5 14 0 13 5 13 0 12 5 12 0 115 110 10 5 10 0 95 90 85 80 75 70 Temp ºC Temp ºF Back Flow and Exhaust sensor characteristics 65 60 55 50 45 40 35 30 25 20 15 10 5 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 2
Functional scheme 11 Functional scheme Fig.
Interior components diagram and parts list 12 Interior components diagram and parts list 12.1 Interior components 1 10 2 11 3 12 4 13 14 5 15 16 17 6 18 7 19 8 20 9 21 6720608836-06.1AL Fig.
Interior components diagram and parts list 6720608836-02.1AL Fig.
Interior components diagram and parts list 12.2 Components diagram 12.2.1 Group 1 9 16 9 15 12 9 13 15 17 14 10 5 6 8 9 7 3 2 11 4 1 6720902973.AB JF Fig.
Interior components diagram and parts list 12.2.2 Group 2 15 27 28 17 13 19 12 30 21 16 20 26 16 18 22 25 13 17 14 23 24 12 19 13 13 27 17 28 35 10 3 2 34 28 31 11 33 8 1 8 5 32 4 8 6 9 7 6720902987.AA JF Fig.
Interior components diagram and parts list Item Description Reference 1 Heat exchanger 8 705 406 419 2 Heat exchanger top gasket 8 704 701 052 3 Condensing exchanger inlet 8 705 700 159 4 Overheat sensor (ECO) 8 707 206 204 5 Heat exchanger bottom gasket 8 704 701 054 6 Site window 8 701 000 401 7 Ignition group 8 701 302 249 8 Heat exchanger O-ring 8 700 205 147 9 Rubber grommet 8 710 303 027 10 Connecting pipe 8 700 715 497 11 Pipe connection clip 8 701 201 028 12 Con
Interior components diagram and parts list 12.2.3 Group 3 5 1 2 4 3 6 9 6 16 13 8 12 11 7 15 14 17 6720902988.AA JF Fig.
Interior components diagram and parts list 12.2.4 Group 4 14 11 10 13 12 11 6 7 9 1 8 5 2 3 4 6720902990.AA JF Fig.
Interior components diagram and parts list 12.2.5 Group 5 1 4 5 12 6 8 2 13 11 7 3 12 4 9 10 9 11 15 16 17 14 (optional) 6720902989.AA JF Fig.
Interior components diagram and parts list 12.2.6 Group 6 4 8 5 6 7 9 10 11 3 2 1 14 15 16 12 13 6720902978.AA JF Fig. 76 Components Diagram Item Description Reference Item Description Reference 1 Control unit - GWH C 920 ES 8 707 207 305 8 Jumper 8 704 401 376 8 707 207 348 1 904 521 342 9 Electrode cables 8 704 401 346 10 Flue gas limiter 8 700 400 032 Cascading kit (optional) 7 709 003 617 1 2 Control unit - GWH C 920 ESC Fuse T2.5A 3 Fuse T1.
Protecting the environment 13 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.
Limited Warranty 14 Limited Warranty 14.1 Limited warranty for GWH C 920 ES residential model General BOSCH tankless water heaters are warranted by the Manufacturer (BOSCH) through Bosch Thermotechnology Corp. 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 Bosch Thermotechnology Corp.
Limited Warranty 14.2 Limited warranty for GWH C 920 ESC commercial model General BOSCH tankless water heaters are warranted by the Manufacturer (BOSCH) through Bosch Thermotechnology Corp. 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 Bosch Thermotechnology Corp.
6720608836 Installer Checklist to be completed by installer upon installation Serial Number ___ ___ ___ ___ ___ ___ ___ ___ (8 digit serial number is located on rating plate on right side panel) Gas Pressure Reading* Static__________ Operating__________ Building Water Pressure __________ Range if on Well system __________ Installing Company _____________________________________________ Installer name _____________________________________________ Address ________________________________________