Faults
Code Cause
of the
error
Description
Checking / solution
DEP-RET>MAX
L11
PCU
Difference between the flow
and return temperatures too
great
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
STB OPEN
L12
PCU
Maximum boiler temperature
exceeded (STB thermostat
maximum)
Bad connection
4
Check the wiring between the PCU PCB and the
STB
4
Check that the SU PCB is correctly in place
4
Check the electrical continuity of the STB
4
Check whether the STB has been correctly fitted
Sensor fault
4
Replace the STB 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
BURNER FAILURE L14
PCU
5 burner start-up failures
Absence of ignition arch
4
Check the wiring between the PCU PCB and the
ignition transformer
4
Check that the SU PCB is correctly in place
4
Check the ionisation/ignition electrode
4
Check the earthing
4
SU PCB faulty: Change the PCB
Presence of the ignition arc but no flame formation
4
Vent the gas flues
4
Check that the gas valve is fully opened
4
Checking the gas supply pressure
4
Check the operation and setting of the gas valve
unit
4
Check that the air inlet and flue gas discharge flues
are not blocked
4
Check the wiring on the gas valve unit
4
SU PCB faulty: Change the PCB
Presence of the flame but insufficient ionization (<3 µA)
4
Check that the gas valve is fully opened
4
Checking the gas supply pressure
4
Check the ionisation/ignition electrode
4
Check the earthing
4
Check the wiring on the ionisation/ignition electrode
8. Troubleshooting
MCA 15 - MCA 25 MCA 25/28 MI
118
29/04/2010 - 300022146-001-B
