BoilerFaultCodesTechnical description
Air pressure switch fault (fan running, but switch not operating or flue/venturi blocked)
What causes this fault?
This fault occurs when the boiler's internal safety sensor cannot confirm that the fan is successfully pushing exhaust gases out of the flue. The most common reasons are a build-up of debris in the small plastic tubes inside the unit or a mechanical failure in the fan or air pressure sensor. Without this confirmation, the boiler refuses to light the gas burner to prevent dangerous fumes from backing up into your home.
This issue is more frequent during periods of heavy wind or storms, as high gusts can sometimes interfere with the pressure balance in the flue system.
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.