Your boiler has stopped working because the fan used to clear out waste gases is not communicating correctly with the main control board.

Incorrect signal from fan

What causes this fault?

This fault occurs when the boiler's main computer loses the ability to accurately control or monitor the speed of the fan. It is usually caused by an internal electronic failure within the fan motor itself or a loose connection in the wiring that carries signals between the fan and the control board. Without a reliable signal, the boiler shuts down as a safety precaution to ensure waste gases are being properly extracted.