BoilerFaultCodesTechnical description
Fan or flue fault (Air pressure switch not proved)
What causes this fault?
This fault occurs when the boiler's safety sensors cannot confirm that the fan is successfully clearing waste gases from the system. The most common reasons are a failing fan motor or a blockage in the small plastic tubes that monitor air pressure, preventing the boiler from firing safely. Exposure to dust or worn bearings in the fan assembly usually triggers this shutdown to prevent carbon monoxide risks.
This issue is more frequent during periods of high wind or extreme cold, as external gusts can disrupt pressure readings and freezing temperatures may cause debris to shift within the flue.
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.