Problem solving
61
830 ES – 6 720 644 936 (2021/08)
9Problem solving
9.1 Error code diagnostics
To remove error code from the display, press the reset button.
Display 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. 67, page 68). Go to steps two and
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 75.
2. Measure resistence loose on wire harness nearby the overmolding, must be 115 -
120 ohm.
3. Check diagnostic menu > 1P, “nC” must be showed on the display.
Backflow temperature
sensor defect - happens if
sensor is disconnected or
short circuit.
1. Check backflow temperature sensor connection. See fig. 67, #1, page 68.
2. Replace exhaust temperature sensor.
3. Check sensor (ref. page 65, chapter 11).
Outlet temperature sensor
fault (Temperature below
36°F or above 210°F).
1. Sensor may trip if water temperature drops below 36°F to protect heater from
freezing conditions. Any damage due to freezing conditions is not covered under
warranty.
2. In areas where water has a high mineral content, periodic descaling may necessary.
3. Check sensor (ref. page 65, chapter 11).
(Flashing) Outlet temperature sensor
not sensing expected
output temperature.
(Status message, not an
error).
1. Check gas pressure. Low gas pressure may prevent the heater from reaching desired
output temperature.
2. Check supply voltage. It must be 120VAC and properly grounded.
3. Possible defective control unit call Bosch Water Heating for further instructions.
Primary fan rotation too low
in operation.
1. Disconnect power supply cord and check wire connection on back side of fan and the
connectors on the control board, see fig. 74, page 75.
2. Check supply voltage. It must be 120VAC and properly grounded.
3. Check venting specifications are met. Long vent lengths, venting with more than
three elbows, blocked vent or combination venting may cause this failure.
4. Ensure intake and exhaust terminations maintain the required clearances stated in
the manual. Cross contamination between intake and exhaust may cause the fan to alter
its rotational speed.
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 from primary fan.
1. Disconnect power supply cord and check wire connections on back side of fan and
the two connectors on the control board, see fig. 74, page 75.
2. Check supply voltage. It must be 120VAC and properly grounded.
3. Possible defective component in fan or defective control unit call Bosch Water
Heating for further instructions.
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