Your boiler's fan is failing to maintain a steady speed, which prevents the system from safely drawing in air and exhausting gases.

Fan speed varies

What causes this fault?

This fault occurs when the boiler's internal computer detects that the fan is spinning at an inconsistent or incorrect speed to safely clear exhaust gases. The most common reason is a mechanical failure within the fan motor or a communication error caused by damaged wiring or a faulty control board. Without a steady and predictable airflow, the boiler shuts down as a safety precaution to prevent improper combustion.