Low
S.21 on Heatline Centurion 25

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

Observe the display to see if the status moves to ignition automaticallyNo action is usually required as this is a normal part of the startup sequenceIf the code persists for several minutes, try resetting the boiler

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