Your boiler has stopped working because it cannot correctly detect the speed of the fan responsible for clearing exhaust gases.

Fan tacho signal fault

What causes this fault?

This fault occurs when the boiler's main computer loses track of how fast the internal fan is spinning, which is a vital safety check before the burner can ignite. The most common reason is a communication failure caused by worn-out bearings in the fan motor or a loose electrical connection in the wiring. Without an accurate speed reading, the boiler shuts down to prevent dangerous exhaust gases from building up inside the unit.