S.08 Low

Vaillant S.08 Fault Code

Also written as S08 — same fault.

The Vaillant S.08 fault code means: your boiler is taking a short, normal break after finishing a heating cycle to prevent overheating and ensure everything cools down properly.. It appears on 31 Vaillant models in our database.

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: Heatingmode:Temporaryshutdownafterheatingprocedure

What causes the Vaillant S.08 fault?

This occurs when the boiler has successfully met the temperature requested by your thermostat and shuts the burner off to prevent the system from getting too hot. It is a built-in safety delay that allows the internal components to cool down and the water to circulate before the boiler is allowed to fire up again. This 'anti-cycling' period is a normal function designed to protect the heat exchanger and improve energy efficiency.

You may notice this status more frequently in spring and autumn when your home requires less intense heat to reach the desired temperature.

DIY fix possible

Wait 5 to 10 minutes for the status code to change automaticallyCheck that your room thermostat is set to the desired temperatureEnsure radiators are turned on to allow heat to dissipate

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Vaillant models that show the S.08 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Vaillant S.08 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026