Low
D.8 on Vaillant Atmomax

Your boiler is receiving a signal from a remote device, such as a thermostat or timer, telling it to turn on and provide heat.

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

External controls heat demand

Shared across the range
This code is shared by the boilers in this range, which use the same control board. It may not be printed in this exact variant’s 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 if your room thermostat is turned up high.Verify if your heating timer or smart app is set to an 'on' period.Lower your thermostat to see if the code disappears, confirming the boiler is simply responding to your settings.

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