Bosch 940 ESO Installation Manual

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6 720 644 956Troubleshooting3710 Troubleshooting10.1 IntroductionMany of the questions customers ask regarding operationof this unit can be answered by following thetroubleshooting steps as outlined below. Visit our web siteat www.boschpro.com for more detailed troubleshootingand service bulletins. For best results, perform each stepbefore proceeding to the next. The suggested solutionsmay require that the cover be taken off. (See Page 7. Fig.3).10.2 Burner does not ignite when hotwater is turned ON1. If the display is blank, verify power to outlet. (120VAC/60Hz properly grounded circuit required). Verify thatthe heater ON/OFF button is turned ON.2. Verify the fuses in the control board are good. SeeSection 7.2, page 25 of the installation manual for fuselocations.3. Make sure cold water inlet connection is plumbed tothe right side of heater when facing unit. See Fig. 25,page 20.4. A minimum of 0.5 gallons per minute (GPM) (1.9 l/m) isrequired to activate the heater. A quart containershould fill in 25 seconds or less to activate heater. Inareas of warm inlet water temperatures, the heater mayincrease activation rate to as high as 1.6 gallons perminute (GPM) to prevent overshooting of settemperature.5. Clean inlet filter screen per chapter 9.2, page 32.6. Inspect the water path for obstructions. Make sure allshowerheads, faucet aerators and whole house filtersare clear of debris.7. The heater activates when the water flow through theunit is at or above the required minimum of 0.5 GPM(1.9 l/m). A crossover in the plumbing creates backpressure on the water flowing through the heater.Therefore, a higher flow rate than normal is needed toforce the heater to activate. To check for a plumbingcrossover, shut off the cold water supply to the waterheater. Then open all of the hot water taps served bythe heater. Wait 10 minutes and check for water flowat taps. There should be no water flowing. Anycontinuous flow of water, small or large, indicates acrossover is present and must be corrected. Consult aprofessional plumber for help in correcting a crossover.Failing single lever faucets and mixing valves arecommon causes of plumbing crossovers.8. With the ON/OFF switch turned to OFF (O) positionand the power supply cord unplugged, remove theunit's front cover (See Page 7. Fig 3). Check wireconnections between the water valve, control unit andelectrode set. See chapter 15.2, page 49 for locationof these parts.9. Water heater in solar mode. If inlet water temperaturesexceed the water heater's set temperature, the burnerswill not ignite and the solar mode indicator will show onthe display. See Fig. 42, page 26.10.3 Water is too hot1. Selected temperature on the unit is set too high. Tolower output temperature, see chapter 8.4, page 27.2. Clean inlet filter screen per chapter 9.1, page 31.3. Inspect the water path for obstructions. Make sure allshowerheads, faucet aerators and whole house filtersare clear of debris.4. Confirm the heater's gas type coincides with the typeof gas being supplied. See Fig. 2, page 6 for locationof rating plate.5. Avoid restrictive outlets. Clean all showerheads andfaucet aerators. It may be necessary to upgrade tohigher flow rate shower heads if allowable by localcode.6. In areas where the water has a high mineral content,periodic descaling may necessary. See chapter 9.3,page 32 for directions.7. Ensure the outlet temperature sensor is making contactand firmly mounted on the hot water pipe.10.4 Water is not hot enough1. Selected temperature on the unit is too low. To raiseoutput temperature, see chapter 8.4, page 27.2. Clean inlet filter screen. See chapter 9.1, page 31.3. Inspect the water path for obstructions. Make sure allshowerheads, faucet aerators and whole house filtersare clear of debris.4. Confirm the heater's gas type coincides with the type ofgas being supplied. See Fig. 2, page 6 for location ofrating plate.5. Check inlet gas particle screen for blockage at gas inletconnection on bottom of unit.6. Verify gas pressure is in accordance with specificationsin chapter 6.6, page 24. A gas pressure reading isneeded to proceed further. Contact your originalinstaller or a local certified gas technician to obtain thisreading.7. Cold water is mixing into the hot water lines (plumbingcrossover). A plumbing crossover can unintentionallyWarning: If you are unable to performthe tasks listed below, or needadditional assistance please contactyour original installer or licensed gastechnician.i Inside the heater it is normal to findunplugged wire connectors. Theseconnections are for adding accessoriessuch as cascading or freeze prevention.