Your boiler is currently running its internal fan to cool down the system after finishing a cycle, which is a normal part of the shutdown process.

Fan over run

What causes this fault?

This occurs when the boiler’s internal heat exchanger needs to shed excess heat after you have finished using a hot water tap. The boiler activates the fan to pull cool air through the unit to prevent internal components from getting too hot. It is a standard safety and maintenance process rather than a mechanical failure.