Your boiler's fan is spinning faster than it should, which means the system has safely shut down to prevent any damage.

Fan speed too high.

What causes this fault?

This fault occurs when the boiler's control system detects that the fan is spinning at an uncontrolled or excessive speed, which prevents the correct mix of air and gas for safe combustion. It is typically caused by a communication failure between the main circuit board and the fan, or a mechanical defect within the fan motor itself. Because the boiler cannot accurately regulate the flame with the fan running too fast, it shuts down as a safety precaution.