Low
S.21 on Vaillant Ecomax Condensing 600/800 series

Your boiler is simply performing a routine check to ensure it is ready to provide hot water quickly, so there is no fault with your system.

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

Pump and fan running (warm start)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

S.20View →

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