BoilerFaultCodesTechnical description
Automatic Lockout. Air Pressure Switch stuck in the On or Off position or wiring 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 is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.