76
ALTERNATING ‘F’ AND ‘5’ - RETURN THERMISTOR FAULT
Remove the Return Thermistor from the CH Return
Pipe and disconnect the wires.
Check the resistance using a suitable multimeter
connected across the thermistor’s terminal pins.
At 25
o
C expect 9,700 - 10,300 Ohms
At 60
o
C expect 2,400 - 2,600 Ohms
At 85
o
C expect 1,000 - 1,100 Ohms
Is the Thermistor value correct?
Is there continuity between the PCB and
the Thermistor?
Fit a new Thermistor
NO
Check and replace
wiring as necessary
YES
NO YES
Replace PCB
77
ALTERNATING ‘F’ AND ‘6’ - OUTSIDE SENSOR FAULT
Disconnect the wires to the outside sensor.
Check the resistance using a suitable multimeter
connected across the Outside Sensor’s terminal pins.
At 0
o
C expect 31,000 - 35,000 Ohms
At 15
o
C expect 15,000 - 16,500 Ohms
At 30
o
C expect 7,700 - 8,500 Ohms
Is the Outside Sensor value correct?
YES
Is the wiring securely connected between the
incoming terminal block boiler connection of the
Outside Sensor and the PCB?
Replace PCB
Fit a new Outside Sensor
NO
Securely connect the wiring at the
Terminal Block and the PCB
Is the wiring securely connected at both the boiler and
Outside Sensor?
YES
NO
Securely connect the wiring at both the
boiler and Outside Sensor
NO
YES
78
ALTERNATING ‘F’ AND ‘7’ - LOW MAINS VOLTAGE
Contact electricity provider
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