Your boiler has detected that the internal fan is spinning faster than it should be when trying to start up, so it has stopped working to keep the system safe.

Fan speed too high at burner start

What causes this fault?

This fault occurs when the boiler's internal computer detects that the fan is spinning at the wrong speed or failing to stop when it should. Because the fan is responsible for clearing out dangerous exhaust gases, the system enters a safety mode and prevents the burner from lighting. The most common reason is a communication error between the fan motor and the main control board, often caused by worn-out electrical components.