Low
S.21 on Heatline Monza

Your boiler is currently performing a routine start-up check of its air extraction system to ensure it is safe to ignite.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description

Pre-run fan

DIY fix possible

Monitor the boiler to see if it moves past this state automaticallyNo action is usually required as this is a normal operating sequenceIf the code persists for several minutes, try a simple reset

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