Your boiler's fan is struggling to spin at the correct speed, which prevents the unit from starting up safely to heat your home.

Fan turning–speed malfunction (too fast at start–up) | Cause: Fan unit obstructed, plug–in fan connector not correctly inserted, Hall sensor defective, fault in cable loom, defective electronic control system

What causes this fault?

This fault occurs when the boiler’s control board detects that the fan is spinning at an incorrect speed, preventing it from safely clearing waste gases from the system. The most common reason is a mechanical failure within the fan motor or a buildup of dust and debris that hinders its movement. It can also be caused by a communication error where the electronic sensors fail to report the fan's speed accurately to the main computer.