Bosch 940 ES Installation And Operating Instructions Manual

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Troubleshooting57940 ES – 6 720 644 930 (2019/09)8 TroubleshootingCAUTION:▶ If you are unable to perform the tasks listed below, or needadditional assistance please contact a qualified gastechnician.8.1 IntroductionMany of the questions customers ask regarding operation ofthis unit can be answered by following the troubleshootingsteps as outlined below. Visit our web site at www.bosch-climate.us for more detailed troubleshooting. For best results,perform each step before proceeding to the next. Thesuggested solutions may require that the cover be taken off.(See fig. 3, page 12).8.2 Burner does not ignite when hot water isturned ONIt is recommended to use “Control board diagnostics” page 56,chapter 7.6 as a tool for problem solving. If the display isshowing a blinking two digit code, refer to this section.1. If the display is blank, verify power to outlet. (120VAC/60Hz properly grounded circuit required). Verify that theheater power button is pressed ON.2. Verify the fuses in the control board are good. To accessfuses, the control board must be removed. Seechapter 5.2, page 46.3. Make sure cold water inlet connection is plumbed to theright side of heater when facing unit. See fig. 32, page 40.4. A minimum of 0.5 gallons per minute (1.9 l/m) of hot waterdemand is required to activate the heater. Confirm at least0.5 gpm flow by timing how long it takes to fill a container.A quart container should fill in 23 seconds or less, from hotwater tap only, to activate heater. In unusual circumstanceswith high inlet water temperatures and low settemperatures, the heater may increase the activation rateabove 0.5 gpm to avoid overheating at low flows. Graduallyincrease water flow (hot water demand) through the heaterto determine if the heater activates with higher flow.5. Clean inlet filter screen per chapter 4.10, page 40.6. Inspect the water path for obstructions. Make sure allshower heads, faucet aerators and whole house filters areclear of debris.7. Check for plumbing crossover. A crossover in the hot andcold plumbing pipes creates back pressure on the waterflowing through the heater. Therefore, a higher flow ratethan normal is needed to force the heater to activate. Tocheck for a plumbing crossover, shut off the cold watersupply to the water heater. Then open all of the hot watertaps served by the heater. Wait 10 minutes and check forwater flow at each tap. There should be no water flowing.Any continuous 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 faucet mixing valves are common causesof plumbing crossovers.8. With the power button pressed switch turned to OFF andthe power supply cord unplugged, remove the unit's frontcover (See fig. 3, page 12). Check wire connectionsbetween the water valve, control unit and electrode set.See chapter 13.2, page 69 for location of these parts.9. Water heater in solar mode. If inlet water temperaturesexceed the water heater's set temperature, the burners willnot ignite and the solar mode indicator will show on thedisplay. See fig. 48, page 47.8.3 Water is too hot1. Selected temperature on the unit is too high. To loweroutput temperature, see chapter 6.4, page 48.2. Clean inlet filter screen per chapter 7.1, page 51 toincrease flow through the heater.3. Inspect the water path for obstructions. Make sure allshower heads, faucet aerators and whole house filters areclear of debris.4. Confirm the heater's gas type coincides with the type of gasbeing supplied. See fig. 2, page 12 for location of ratingplate.5. Avoid restrictive outlets. Clean all shower heads and faucetaerators. It may be necessary to upgrade to higher flow rateshower heads if allowable by local code.6. In areas where the water has a high mineral content,periodic descaling may necessary. See chapter 7.3,page 52 for directions.8.4 Water is not hot enough1. Selected temperature on the unit is too low. To raise outputtemperature, see chapter 6.4, page 48.2. Clean inlet filter screen. See chapter 7.1, page 51 toincrease flow through the heater.3. Inspect the water path for obstructions. Make sure allshowerheads, faucet aerators and whole house filters areclear of debris.4. Confirm the heater's gas type coincides with the type of gasbeing supplied. See fig. 2, page 12 for location of ratingplate.5. Check inlet gas particle screen for blockage at gas inletconnection on bottom of unit.