Your boiler is simply preparing its internal pump before starting the heating process, which is a normal part of its operation.

Heatingmode:Pumppre-run

What causes this fault?

This code appears when the boiler's control board sends power to the internal pump to begin circulating water before the burner ignites. It is a brief safety and efficiency check designed to push any air or cold water out of the heat exchanger. This is a normal part of the start-up sequence and does not mean your boiler has broken down.