Your boiler has detected an internal safety shutdown because the fan that clears exhaust gases is not running.

Fan does not run. Possible causes: Hot water high limit stat tripped, Safety limit stat tripped, control board, ignition board, air pressure switch, or fan manual failure.

What causes this fault?

This fault occurs because the boiler's safety sensors have detected that the internal fan isn't moving air safely through the system. This is often caused by a mechanical failure of the fan motor itself or a triggered safety switch that has cut power to prevent overheating. Without the fan running to clear exhaust gases, the boiler will automatically shut down as a protective measure.