Your boiler is simply finishing its cooling process after providing hot water and is operating exactly as it should.

DHWmode: Pump overrun

What causes this fault?

This fault occurs when the boiler detects water flowing backwards through the internal system or senses an unusual pressure change when the pump starts. The most common reason is a blockage in the pipework or a failing non-return valve that is stuck open, allowing water to move in the wrong direction. It can also be triggered if the pump itself is struggling to circulate water effectively through the heat exchanger.