Low
S.21 on Vaillant Turbomax Plus 828

Your boiler is currently warming up its internal components to make sure hot water is available quickly when you turn on the tap.

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.

What the manual says

Manufacturer manual

Fan running (warm start)

From this model's manual
Verified against the Vaillant Turbomax Plus 824 828e installation & service manual, page 38.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

DIY fix possible

Check if your hot water is working as normalIdentify if the 'Warm Start' function is enabled (often a small LED or dial setting)Turn off the Warm Start function if you wish to save energy and stop the fan from running periodically

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Related fault codes

S.20View →S.24View →S.28View →

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