Low
S.21 on Vaillant ecoTEC exclusive System

Your boiler is currently going through its normal starting sequence to begin heating 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.

What the manual says

Manufacturer manual

DHW mode: Fan start-up

From this model's manual
Verified against the Vaillant Ecotec Exclusive Combi installation & service manual, page 42.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

What causes this fault?

This is a normal operational status that occurs when your boiler prepares to provide heat or hot water. It means the internal fan is spinning up to the correct speed to ensure there is enough air for the combustion process to begin safely. Once the fan reaches the required speed, the boiler will proceed to the next stage of ignition.

DIY fix possible

This fault may be fixable without an engineer. Check your manual first.

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