Your boiler's internal pump is running longer than it should after the heating has switched off, which often indicates a communication error or a trapped signal.

Pump over-run time (CH mode)

What causes this fault?

This fault occurs when the boiler's internal computer keeps the water pump running indefinitely because it hasn't received the signal to tell it the heating cycle has finished. The most common reason is a communication error between the main circuit board and the pump, or an electrical component on the board getting stuck in the 'on' position. While the boiler may still function, this constant running puts unnecessary wear on the pump and wastes electricity.