Your boiler is performing a routine check of the internal pump to ensure water is flowing correctly before it starts the main heating process.

Pump pre run

What causes this fault?

This code appears when the boiler initiates a brief test cycle to ensure the internal pump is moving water through the heat exchanger before the burner ignites. It is a standard safety and performance check to prevent the unit from overheating during the start-up phase. Under normal conditions, this is a routine operation and does not indicate a breakdown.