Low
S.21 on Heatline Compact 30

Your boiler is currently checking that its internal air extraction system is working correctly before it attempts to ignite the flame.

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

No action required; this is a normal operational status messageMonitor the display to see if it progresses to a flame symbolIf the code persists for several minutes without ignition, try a reset

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