Problem solving | 43
6 720 644 887 (2013/02)C 1210 ES/ESC
9 Problem 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. 76, page 51). 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. 83, #7, page 59.
2. Measure resistance 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. 76, #1, page 51.
2. Replace exhaust temperature sensor.
3. Check sensor (ref. page 48, chapter 11).
Outlet temperature sensor fault
(Temperature below 36°F or above 210°F).
1. Check wire connection at hot water temperature sensor. See fig. 82, page 58.
2. 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.
3. In areas where water has a high mineral content, periodic descaling may
necessary.
4. Check sensor (ref. page 48, chapter 11).
(Flashing) Outlet temperature sensor not sensing
expected output temperature.
(Status message, not an error).
1. Check wire connection at hot water temperature sensor, see fig. 82, page 58.
2. Check gas pressure. Low gas pressure may prevent the heater from reaching
desired output temperature.
3. Check supply voltage. It must be 120VAC and properly grounded.
4. Possible defective control unit call Bosch Water Heating for further
instructions.
Table 39
* By installer or service technician only.
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