Bosch 940 ES Installation And Operating Instructions Manual

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Problem solving940 ES – 6 720 644 930 (2019/09)609 Problem solving9.1 Error code diagnosticsTo remove error code from the display, press the reset button.Display Cause SolutionFault in the flue gas limiter.Temperature above 230°F(110 °C) inside the cabinet.1. Check continuity of the flue gas limiter (see fig. 67, page 67). Go to steps twoand three to determine flue gas limiter fault and repair it.2. Check for flue gas leakage around the top and bottom seals of heat exchanger,use mirror to check around the rear as well as the viewing window.3. Check that flue gas limiter connector and spade connections are secure.4. Unplug heater and check the wiring harness connections on the control board.Wire harness defect. 1. Check wire harness, see fig. 74, #7, page 74.2. Measure resistence loose on wire harness nearby the overmolding, must be115 - 120 ohm.3. Check diagnostic menu > 1P, “nC” must be showed on the display.Backflow temperature sensordefect - happens if sensor isdisconnected or short circuit.1. Check backflow temperature sensor connection. See fig. 67, #1, page 67.2. Replace exhaust temperature sensor.3. Check sensor (ref. page 64, chapter 11).Outlet temperature sensor fault(Temperature below 36°F orabove 210°F).1. Sensor may trip if water temperature drops below 36°F to protect heater fromfreezing conditions. Any damage due to freezing conditions is not covered underwarranty.2. In areas where water has a high mineral content, periodic descaling maynecessary.3. Check sensor (ref. page 64, chapter 11).(Flashing) Outlet temperature sensor notsensing expected outputtemperature.(Status message, not an error).1. Check gas pressure. Low gas pressure may prevent the heater from reachingdesired output temperature.2. Check supply voltage. It must be 120VAC and properly grounded.3. Possible defective control unit call Bosch Water Heating for furtherinstructions.Primary fan rotation too low inoperation.1. Disconnect power supply cord and check wire connection on back side of fanand the connectors on the control board, see fig. 74, page 74.2. Check supply voltage. It must be 120VAC and properly grounded.3. Check venting specifications are met. Long vent lengths, venting with morethan three elbows, blocked vent or combination venting may cause this failure.4. Ensure intake and exhaust terminations maintain the required clearancesstated in the manual. Cross contamination between intake and exhaust maycause the fan to alter its rotational speed.5. Check gas pressure. Low gas pressure may cause the fan to change its speedto meet desired temperature.6. Possible defective control unit call Bosch Water Heating for furtherinstructions.