Your boiler has stopped working because the internal fan that moves waste gases out of the flue is not spinning.

The fan is stationary and open circuit.

What causes this fault?

This fault occurs when the boiler's control system attempts to start the fan but detects no electrical life or movement from the motor. The most common reason is that the fan motor has burnt out or suffered a mechanical seizure, though it can also be caused by loose wiring or the main circuit board failing to send power to the component.