Low
d.16 on Vaillant Home System

This is a status indicator rather than a fault, showing whether your external heating controls are currently asking the boiler to turn on or stay 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 Home System installation & service manual.
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 is turned up higher than the current room temperatureEnsure your programmer or heating app is set to an 'On' periodReplace the batteries in your wireless room thermostat if the screen is blank

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Related fault codes

S.0View →d.18View →

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