Your boiler is performing a routine self-check of the internal pump before starting the burner to ensure water is circulating correctly.

Pump pre run

What causes this fault?

This is a normal part of the boiler's startup process and occurs when the system sends power to the internal pump to get water moving. It happens every time you ask for heating or hot water to confirm the pump is spinning correctly before the flames ignite. It is not an error, but rather a brief verification step the internal computer performs to ensure the system is safe to operate.