Low
S.20 on Vaillant Atmomax

Your boiler has received a request to provide hot water, but it is taking longer than expected to start the heating process.

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 requirement error

DIY fix possible

Check if any hot water taps have been left slightly openEnsure your thermostat is calling for heat correctlyTry resetting the boiler by turning the main power dial off and back on

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Related fault codes

S.10View →S.14View →

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