4.6 FLAME ON BEFORE GAS VALVE ON
4.7 FLOW THERMISTOR FAULT
4.8 OUTSIDE SENSOR FAULT
Restart the boiler, does boiler work OK?
Disconnect the electrical connection to the Flow
Thermistor and check the resistance using
a suitable multimeter connected across the
thermistor’s terminal pins.
At 25°C expect 9,700 - 10,300 Ω
At 60°C expect 2,400 - 2,600 Ω
At 85°C expect 1,000 - 1,100 Ω
Is the thermistor value correct?
Disconnect the wires to the Outside Sensor.
Check the resistance using a suitable multimeter
connected across the thermistor’s terminal pins.
At 0°C expect 31,000 - 35,300 Ω
At 15°C expect 15,000 - 16,500 Ω
At 30°C expect 7,700 - 8,500 Ω
Is the thermistor value correct?
Disconnect the electrical connection to the Flame
Sense Electrode. Is there continuity between the
Electrode and earth?
Is there continuity in the wiring from the primary PCB to
the Thermistor? (8 way connector, connections 3 and
4, black and pink)
Does the Outside Sensor wiring between the boiler
terminal strip and the PCB have continuity and is it
securely connected (5 way low voltage connector,
connections 4 and 5, grey and black wires)?
Is the wiring securely connected at both the boiler and
Outside Sensor?
Replace wiring from primary PCB to ame sense
electrode
Replace primary PCB
Replace main PCB
No
Yes
Yes
Yes
No
No
No
No
Yes
Yes
Yes
Yes
No
No
Check integrity of wiring from primary PCB to Flame
Sense electrode, replace if deteriorated. Check condition
of Flame Sense Electrode and replace if deteriorated
Fit a new thermistor
Fit a new outside sensor
Replace Flame Detection Electrode
Replace wiring from ow thermistor to
primary PCB
Ensure the wiring has continuity and is
securely connected
Securely connect the wiring at both the
boiler and Outside Sensor
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