Your boiler has stopped working because the internal fan that safely removes exhaust gases is not running correctly.

Fan fault detected by diagnostic feature.

What causes this fault?

This fault occurs when the boiler's safety system detects that the fan isn't spinning fast enough to clear waste gases from the flue. The most common reasons are mechanical wear in the fan motor bearings or a build-up of debris that prevents the blades from turning freely. Occasionally, the sensor that monitors the fan’s performance may be faulty, causing the boiler to shut down as a precaution.