Low
S.21 on Vaillant Home System

Your boiler is performing a routine start-up check by running its internal fan before beginning to heat your water.

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

Hot water handling mode: Advance fan operation

DIY fix possible

No action requiredWait for the status code to change automatically as the heating process continues

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Related fault codes

S.20View →S.22View →S.24View →

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