BoilerFaultCodesVaillant S.06 Fault Code
Also written as S06 — same fault.
The Vaillant S.06 fault code means: your boiler is simply cooling itself down after providing heating and will return to normal operation shortly.. It appears on 12 Vaillant models in our database.
Technical description: Heating mode: Fan overrun. The fan overrun for heating mode is activated.
What causes the Vaillant S.06 fault?
This occurs when the boiler has finished heating your home and needs to blow its internal fan for a short period to remove any remaining heat from the heat exchanger. It is a safety feature that protects the internal components from overheating after the burner has turned off. Your boiler has not actually failed; it is simply performing a standard cooling cycle before it can start again.
This status is more frequently seen during winter when the heating is working hard and the boiler is reaching higher internal temperatures.
DIY fix possible
Wait for a few minutes as this is a normal part of the boiler's operation cycleCheck that your thermostat is set to the desired temperatureEnsure your radiator valves are open to allow heat to dissipate
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Vaillant models that show the S.06 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant S.06 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
- Vaillant ecoFIT Pure 425 manual (PDF)
- Vaillant ecoFIT Pure 435 manual (PDF)
- Vaillant ecoFIT Pure 835 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026