Your boiler is simply taking a moment to cool itself down after heating your water, which is a normal part of its operation.

DHW mode: Pump/fan overrun. The pump/fan overrun for domestic hot water mode is activated.

What causes this fault?

This occurs because the boiler has just finished heating your taps or shower and needs to move heat away from the internal components. The pump and fan continue to run briefly to dissipate this residual heat and protect the system from overheating. It is a standard safety feature rather than a mechanical failure.