Your boiler has stopped working because the internal fan is not spinning at the correct speed or the system cannot communicate with it.

Incorrect signal from fan

What causes this fault?

This fault occurs when the boiler's main control board sends a request for the fan to spin, but the fan either fails to move or cannot report its speed back correctly. The most common reasons are a buildup of dust and debris seizing the fan bearings, a loose connection in the internal wiring, or a failure in the electronic components that control the motor.