Code Faults Cause
of the
fault
Description Checking / solution
L04 DEF.OUTLET S.
PCU Temperature of heat exchanger
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
L05 STB EXCHANGE
PCU Exchanger 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
L06 BACK S.FAILURE
PCU The return temperature sensor has
short-circuited
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
L07
BACK S.FAILURE
PCU The return temperature sensor is
on an open circuit
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
Diematic iSystem For C 330 / C 630 ECO 7. Troubleshooting
31082018 - 7600691-001-06
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