Your boiler's fan is running longer than it should after the heating has turned off, which is usually a sign of a communication error between internal components.

What causes this fault?

This fault occurs when the boiler's internal computer stays in a cooling phase for too long because it can no longer accurately track the fan's speed. The most common reason is a communication breakdown where the control board receives incorrect signals from the fan, causing the system to keep the fan running as a safety precaution. Over time, heat stress or moisture can degrade the electrical connections or the sensitive circuitry within the fan motor itself.