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MCA 35
Code Faults
L11
RET-DEP>MAX
L12
STB OPEN
BURNER FAILURE PCU
L14
15/06/12 - 300022160-001-01
Cause
Description
of the
fault
PCU
Difference between the flow
and return temperatures too
great
PCU
Maximum boiler temperature
exceeded (STB thermostat
maximum)
5 burner start-up failures
Checking / solution
Sensor fault
Check the Ohmic value of the sensor
4
Replace the sensor if necessary
4
Bad connection
Check that the sensor has been correctly fitted
4
No water circulation
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
4
Bad connection
Check the wiring between the PCU PCB and the
4
STB
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
4
Sensor fault
Replace the STB if necessary
4
No water circulation
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
No ignition
Check the wiring between the PCU PCB and the
4
ignition transformer
Check that the SU PCB is correctly in place
4
Check the ionization/ignition electrode
4
Check the earthing
4
SU PCB faulty: Change the PCB
4
Ignition arc, but no flame formation
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
4
unit
Check that the air inlet and flue gas discharge flues
4
are not blocked
Check the wiring on the gas valve unit
4
SU PCB faulty: Change the PCB
4
Presence of the flame but insufficient ionization (<3 µA)
Check that the gas valve is fully opened
4
Checking the gas supply pressure
4
Check the ionization/ignition electrode
4
Check the earthing
4
Check the wiring on the ionization/ignition
4
electrode
8. Troubleshooting
111
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