Your boiler has stopped working because the internal fan, which safely exhausts gases, is unable to start or spin at the correct speed.

Lights: Flash Flash On. NOTE: The fan is supplied with 325 Vdc. Check continuity from N to O & from P to Q on 3-way PCB connector. Check continuity from R to S & from T to U & from V to W on smaller 6-way PCB connector.

What causes this fault?

This fault occurs when the boiler's control board cannot detect the fan spinning at the speed required to safely clear waste gases from the system. The most common physical causes are a buildup of dirt or debris in the fan blades, a complete motor failure, or a loose electrical connection between the fan and the main circuit board.