FAULT FINDING AND DIAGNOSIS
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8.1 Fault finding
Blue light
indication
Fault Possible solution/check
No light No power at control
board
▶Check
– Mains supply voltage to the appliance.
– Appliance mains switch is ON.
– Fuse F1 - 2A Slow blow.
▶ Replace control board.
Light ON Appliance ON but not
operating during demand
▶Check
– Live demand at ST2 terminal (L
R
) - is there a demand?
– Manual bypass is open.
– If Central Heating is working, check Hot Water controls.
– If Hot Water is working, check Central Heating controls (i.e. external diverter valve, room
thermostat/programmer, frost thermostat).
▶ Replace control board.
Slow flash
(mostly off,
flashes on)
Ignition lockout ▶Check
– Gas present and at the correct pressure?
– Gas valve:
• Is there 29V d.c. to each solenoid?
• The resistance of each solenoid ( 9.3.4).
– Combustion CO2 level.
– Blockage or restriction in the flue.
– Gas valve adjustment.
– Ignition electrodes/harness/connections.
• Condition and resistance of the leads (approximately 2,100 Ω).
▶ Replace control board.
Slow flash
(mostly on,
flashes off)
Flue overheat Flue temperature too high.
▶ Check heat exchanger baffles are correctly fitted or removed and not refitted
Heat exchanger overheat ▶Check
– Water pressure.
– All air is vented.
– Pump/harness/connections.
–Water leaks/blockage.
– Safety thermostats/low voltage wiring harness/connections.
– Blocked heat exchanger.
▶ Replace control board.
Flue pressure switch ▶ Check for blockage in the flue system.
Fast flash Volatile lockout (sensor,
fan or code plug)
▶Check
– Temperature sensors:
• Condition and resistance of the leads.
• Resistance of sensor ( 9.3.1).
–Fan.
• 230V A.C. across the live (purple) and neutral (brown)
– Fan lead continuity.
–Code plug.
• Is code plug missing or not inserted properly?
2 pulses ▶Check
– Service mode switch is in “MIN” position?
▶ Return mode switch to “NORM” position if minimum test mode not required.
5 pulses ▶Check
– Service mode switch is in “MAX” position?
▶ Return mode switch to “NORM” position if maximum test mode not required.
Table 35 Fault finding
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