Low
D.5 on Vaillant Atmomax

Your boiler is currently waiting for the water to reach the correct temperature before it begins its next heating cycle.

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

Set value of flow temperature or target value of return

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 that your room thermostat is turned upEnsure all radiator valves (TRVs) are openWait 10-15 minutes to see if the boiler fires up automatically

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Boiler cover options

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