Low
S.21 on Heatline Capriz Plus

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 ensure it progresses to ignition (S.4)If the code stays on screen indefinitely, try a resetIf the boiler fails to fire after this stage, contact a Gas Safe engineer

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Related fault codes

F.22View →

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