Your boiler is currently set to run the pump continuously, which is usually a configuration setting rather than a breakdown.

What causes this fault?

This occurs because the boiler’s internal software has been configured to keep the pump running all the time instead of only when heat is needed. It is typically caused by a specific setting being changed during a service or installation, rather than a mechanical failure of a part. While the boiler will still provide heat and hot water, the pump will continue to circulate water around the system indefinitely.