Your boiler is performing a routine safety check by running the fan before the burner ignites.

fan pre-run

What causes this fault?

This status occurs when the boiler prepares for ignition by clearing out the combustion chamber. The fan spins up to ensure there is a safe flow of fresh air and to remove any residual gases before the burner light. It is a fundamental part of the boiler's start-up sequence and not a sign of a mechanical failure.