Short answer
A gas valve fault means the valve fails to open, fails to modulate correctly, or fails to close tightly. Symptoms range from ignition lockouts to unstable combustion and, rarely, gas let-by. Gas valves are safety-critical and should be replaced, not repaired.
Common causes
Coil failure or open circuit.
Debris on the valve seat or inlet filter.
Incorrect offset or throttle setting after a previous repair.
Low inlet pressure masquerading as a valve fault.
What the engineer checks
Measure coil resistance and the supply voltage to the valve during ignition.
Check inlet and outlet pressure.
Carry out a let-by test where applicable.
Repair and prevention
Replace the valve, set offset and throttle to the manufacturer's procedure, and complete a full combustion analysis at minimum and maximum rate.
Figures are typical for UK natural gas. The current edition of the relevant IGEM standard and the manufacturer's instructions always take precedence on site.
Need this done on site?
Manufacturer support
We diagnose this fault on all major commercial boiler brands:
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