S.36 Low

Vaillant S.36 Fault Code

Also written as S36 — same fault.

The Vaillant S.36 fault code means: your boiler is currently waiting for a signal from your thermostat and isn't receiving a request to turn the heating on.. It appears on 34 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: Not heating demand form low voltage

What causes the Vaillant S.36 fault?

This code appears when the boiler is powered on and ready to work but has not received a command from your room thermostat or programmer to start heating. It usually indicates that the target temperature in your home has already been reached or that there is a communication break between your controls and the boiler. Common culprits include dead batteries in a wireless thermostat or a loose connection in the external wiring.

This is frequently seen during the transition into autumn when homeowners first turn their heating back on only to find their thermostat batteries have drained over the summer.

Typical repair cost £0-120 (including labour)

DIY fix possible

Check that your room thermostat is turned up higher than the current room temperature.Ensure your heating programmer or central heating timer is set to 'On' or 'Auto'.Replace the batteries in your wireless wall thermostat if the screen is blank or showing a low battery icon.

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Vaillant models that show the S.36 fault code

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

Source

Vaillant S.36 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