Low
S.31 on Vaillant ecoTEC Combi

Your boiler is currently set to summer mode, which means it will provide hot water to your taps but will not turn on your central heating radiators.

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

Central heating thermostat knob turned off or no heat demand by the eBUS control unit

From this model's manual
Verified against the Vaillant Ecotec installation & service manual, page 43.
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 status occurs because the central heating function has been manually deactivated, often by turning the heating control dial all the way to the left. It signifies that the boiler is intentionally ignoring requests for heating while remaining ready to provide hot water. In some cases, this may also be triggered by an external smart controller or weather compensation sensor telling the boiler that heat is not required.

This is most common during the spring and summer months when homeowners intentionally disable their radiators to save energy.

DIY fix possible

Locate the radiator symbol button or dial on the boiler control panel.Increase the heating temperature setting or turn the dial clockwise.Ensure your room thermostat is turned up to a temperature higher than the current room temperature.

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