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.

What the manual says

Manufacturer manual

Pre-run fan

From this model's manual
Verified against the Heatline Monza installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

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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