Your boiler's hot water pump is running for too long, which usually means the system is struggling to cool down or a sensor is misreading the temperature.

What causes this fault?

This fault occurs when the boiler detects that the hot water pump is working for longer than expected to cool the internal heat exchanger. It usually happens because a temperature sensor is sending incorrect readings or the pump itself is struggling to circulate water effectively through the system. If the heat cannot be moved away from the boiler quickly enough, the system triggers this code as a safety precaution.