Code Faults Cause
of the
fault
Description Checking / solution
L08 BACK S.FAILURE
PCU Return temperature too low Bad connection
4 Check the wiring between the PCU PCB and the
sensor
4 Check that the SU PCB is correctly in place
4 Check that the sensor has been correctly fitted
Sensor fault
4 Check the Ohmic value of the sensor
4 Replace the sensor if necessary
No water circulation
4 Vent the air in the heating system
4 Check the circulation (direction, pump, valves)
4 Check the water pressure
4 Check the cleanliness of the heat exchanger
L09 STB BACK
PCU Return temperature too high Bad connection
4 Check the wiring between the PCU PCB and the
sensor
4 Check that the SU PCB is correctly in place
4 Check that the sensor has been correctly fitted
Sensor fault
4 Check the Ohmic value of the sensor
4 Replace the sensor if necessary
No water circulation
4 Vent the air in the heating system
4 Check the circulation (direction, pump, valves)
4 Check the water pressure
4 Check the cleanliness of the heat exchanger
L10 DEF.DT.ECH.RET
PCU Difference insufficient between the
exchanger temperature and the
return temperature
Sensor fault
4 Check the Ohmic value of the sensor
4 Replace the sensor if necessary
Bad connection
4 Check that the sensor has been correctly fitted
No water circulation
4 Vent the air in the heating system
4 Check the circulation (direction, pump, valves)
4 Check the water pressure
4 Check the cleanliness of the heat exchanger
4 Check that the heating pump is operating
correctly
7. Troubleshooting Diematic iSystem For C 330 / C 630 ECO
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31082018 - 7600691-001-06
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