Low
D.90 on Vaillant Atmomax

Your boiler is currently communicating with an external room thermostat or digital controller, and this code is simply a status update rather than a mechanical fault.

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

Digital regulator status

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 your room thermostat is turned up and calling for heatEnsure the batteries in your wireless thermostat are freshRestart the boiler once to refresh the digital connection

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Related fault codes

D.91View →F.49View →

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