Your boiler's fan is not spinning at the correct speed, which prevents the system from safely clearing exhaust fumes and starting the ignition process.

Fan fault

What causes this fault?

This fault occurs when the boiler's control system detects that the fan is either not spinning at all or is rotating at the wrong speed to safely vent exhaust gases. The most common reason is a mechanical failure within the fan motor or a communication break between the electronic control board and the fan assembly.