Your boiler is preparing to ignite but is stuck at the stage where the internal fan is spinning up to clear the combustion chamber.

Fan running

What causes this fault?

This status occurs when the boiler is attempting to start its ignition sequence but becomes stuck while the fan is spinning. It typically happens because the fan cannot reach the required speed or the boiler's control board fails to receive a signal confirming that the fan is working correctly. This prevents the boiler from safely moving to the next stage of lighting the burner.