Your boiler's internal fan isn't spinning fast enough to safely clear away exhaust fumes, causing the system to shut down for your protection.

Airflow stopped during operation

What causes this fault?

This fault occurs when the boiler's control system detects that the internal fan is spinning slower than the required safety threshold. The most common reason is a buildup of dirt or mechanical wear within the fan motor itself, though it can also be caused by loose electrical connections or a failing control board failing to send the correct signal.