Your boiler has stopped working because the internal fan that safely removes exhaust gases is either stuck or not communicating correctly with the system.

Fan error

What causes this fault?

This fault occurs when the boiler's control system detects that the internal fan is not spinning at the correct speed or has failed to start entirely. The most common reason is that the fan motor has burnt out or become seized, though it can also be caused by a communication failure between the fan and the main circuit board.