Your boiler is currently stuck in a checking stage where the fan is running but the burner has not yet lit.

fan pre-run

What causes this fault?

This fault occurs when the boiler's control system is waiting for confirmation that the fan is spinning at the correct speed to safely clear out gases before ignition. The most common reason is that the fan has become worn or blocked, or the circuit board is failing to receive the electrical signal required to move to the next step of the starting process.