Your boiler is continuing to run its internal fan or pump for a short period to safely cool down after the heating or hot water has been turned off.

pump / fan overrun

What causes this fault?

This occurs when the boiler has finished heating your home and needs to dissipate residual heat from the internal components to prevent overheating. The system keeps the pump or fan running for a few minutes to circulate water or air until the temperature drops to a safe level. It is a standard safety feature of the appliance rather than a mechanical failure.