Low
d.16 on Vaillant ecoTEC sustain

Your boiler is correctly receiving a signal from your thermostat that the heating is currently turned off.

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 24V room thermostat: off=Heating off, on=Heating on

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 wall-mounted thermostat or smart app settings to ensure they are set to 'on' or 'active'Increase the target temperature on your room thermostat to see if the boiler status changes to 'on'Check batteries in your wireless thermostat unit if applicable

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Related fault codes

d.15View →d.17View →

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