Your boiler has detected that the internal fan responsible for safely venting fumes is not communicating correctly with the main control board.

Incorrect signal from fan

What causes this fault?

This fault occurs when the boiler's internal computer detects that the fan is not spinning at the correct speed to safely expel waste gases. It is usually caused by a mechanical failure within the fan motor or a buildup of dirt and debris that prevents the blades from turning freely. In some cases, the plastic tubes that measure air pressure can become blocked or split, sending a false 'stop' signal to the system.