Faults
Code Cause
of the
error
Description
Checking / solution
DEF.OUTLET S.
L03
PCU
The boiler flow 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
DEF.OUTLET S.
L04
PCU
Boiler temp 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
STB OUTLET
L05
PCU
Boiler 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
BACK S.FAILURE
L06
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
8. Troubleshooting
MCA 15 - MCA 25 MCA 25/28 MI
116
29/04/2010 - 300022146-001-B