Your boiler's fan is not spinning fast enough to safely start the burner, causing the system to shut down for safety.

Burner in fault state. Fan speed too low at burner start. Cause: Check the fan, check the fan cables and supply, check the fan control. Press E.

What causes this fault?

This fault occurs when the boiler's internal computer tries to start the heating process but detects that the fan isn't reaching the necessary speed to clear out exhaust gases. The most common reasons are a build-up of debris causing the fan to stick, a failure in the fan's motor, or a loose electrical connection between the fan and the main control board.