Low
S.31 on Vaillant ecoTEC Pro / ecoTEC Plus

Your boiler is currently set to only provide hot water and is ignoring your request for central heating.

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

No heat demand boiler in summer operating mode

From this model's manual
Verified against the Vaillant Ecotec Combi 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 code appears when the boiler's internal settings have been adjusted to keep the central heating turned off, usually via the control dial or digital menu. While the unit will still provide hot water for your taps, it is intentionally ignoring any signals from your thermostat to warm up the radiators. It is often triggered accidentally when someone tries to turn the heating down and inadvertently switches the system into a 'hot water only' mode.

This is very common in early autumn when homeowners forget they switched the boiler to summer mode several months prior and try to turn the heating back on for the first time.

DIY fix possible

Locate the radiator symbol button or dial on the boiler control panelIncrease the heating temperature setting above 0 or 'Off' until a temperature appearsCheck that your room thermostat is turned up higher than the current room temperature

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