Your boiler has stopped working because the fan that helps remove waste gases is not spinning or communicating correctly with the system.

The fan is not functioning properly; check the connectors and the fuse of the transformer and check the voltage on the control panel connector.

What causes this fault?

This fault happens when the boiler's internal computer tries to start the fan to clear out exhaust gases but detects that the blades aren't spinning. It is usually caused by a mechanical failure in the fan motor, loose wiring between the components, or a blown fuse that has cut off power to the fan. Without a working fan to safely remove fumes, the boiler will stay switched off as a safety precaution.