Medium
S.059 on Vaillant ecoTEC Plus 836

Your boiler is temporarily preventing itself from firing up because it cannot detect enough water flowing through the system to heat it safely.

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

Heatdemandavailable.Thecirculationwatervolumeisnotsufficientforaburnerstart.

From this model's manual
Verified against the Vaillant Ecotec Plus installation & service manual, page 79.
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

Ensure all radiator valves are fully openCheck that your external heating controls are calling for heatCheck your boiler's pressure gauge and ensure it is between 1 and 1.5 bar, topping up via the filling loop if necessary

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