Medium
D.35 on Vaillant Atmomax

Your boiler is struggling to bring the heating up to temperature, likely because there is air trapped in the system or the water pressure is too low.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

What the manual says

Manufacturer manual

Not relevant

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 the pressure gauge and top it up to 1.5 bar using the filling loopBleed all radiators in the house to release trapped airOnce bled and topped up, restart the boiler

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