Your boiler has stopped working because the fan that removes waste gases cannot start or is not being powered correctly.

Fan does not run: Fan defective or improperly fitted (mechanically or electrically). Fuse F2 (3.15 AT) defective. Transformer defective (power on X3?). electrical connections mixed up; electrical connections interrupted.

What causes this fault?

This fault occurs when the boiler's control system attempts to start the fan to clear waste gases but detects no movement. The most common cause is either a mechanical failure within the fan motor or a blown internal fuse that has cut off the power supply to the component. In some cases, it can also be triggered by a faulty transformer or loose wiring connections that prevent the electrical signal from reaching the fan.