High
F.33 on Glow-worm HXi

Your boiler has stopped working because it cannot confirm the fan is running safely, often triggered by extremely cold weather or a sensor issue.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Fan frost protection function active – air pressure switch fault

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

F.22View →F.23View →F.24View →

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