Low
d.08 on Vaillant ecoTEC sustain

Your boiler is currently receiving a signal from your room thermostat telling it that no heating is required at this moment.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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

Status of the 230V thermostat: 0=Room thermostat open (no heat requirement), 1=Room thermostat closed (heat requirement)

From this model's manual
Verified against the Vaillant Ecotec Sustain installation & service manual, page 47.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

DIY fix possible

Check your room thermostat to ensure the target temperature is set higher than the current room temperatureEnsure your thermostat is not in sleep or frost protection modeCheck the battery levels in your wireless thermostat if applicable

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