Your boiler is briefly keeping the internal parts running to cool itself down after heating your home or water.

pump / fan overrun

What causes this fault?

This is a normal operational state where the boiler continues to run the pump and fan for a few minutes after the burner has turned off. It physically moves excess heat away from the primary heat exchanger to prevent internal components from overstressing or overheating once your house is warm. This ensures the boiler cools down safely and is ready for the next time you need heating or hot water.