Your boiler is trapped in a cooling-down cycle where the fan keeps running longer than necessary, preventing it from starting a new heating cycle.

Heating system fan over run

What causes this fault?

This fault occurs when the boiler's control board fails to receive a signal that the fan has slowed down or stopped after a heating cycle, causing it to stay in a permanent cooling mode. The most common reason is a malfunctioning relay on the main circuit board or a faulty fan that is sending incorrect speed data back to the system. While the boiler is stuck in this 'over run' phase, it will refuse to ignite for central heating or hot water because it believes it hasn't finished cooling down.