BoilerFaultCodesYour boiler has stopped working because its internal safety switch is stuck and cannot confirm it is safe to start the burner.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Lockout Burner Mains - Automatic APS Stuck Fault
What causes this fault?
This fault occurs when the boiler's internal safety sensor, called the Air Pressure Switch, is stuck in the 'on' position before the fan has even started. The boiler refuses to fire up because it cannot confirm that harmful exhaust gases are being safely cleared through the flue. The most common reasons are a build-up of debris or moisture in the small sensing tubes, or a mechanical failure within the switch itself.
This fault is more frequent during autumn and winter, as heavy winds can cause pressure fluctuations in the flue, and colder temperatures can lead to moisture condensation blocking the sensing tubes.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
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A boiler cover plan would cover faults like APS Stuck Fault — no call-out fees, no surprises.
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