Medium
S.53 on Vaillant ecoFIT Pure 435

Your boiler has temporarily stopped because it cannot circulate water efficiently, likely because the pressure is too low or a valve is blocking the flow.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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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

Product in waiting period/operation block function due to low water pressure (flow/return spread too large)

From this model's manual
Verified against the Vaillant Ecofit Pure 830 installation & service manual, page 33.
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 boiler pressure gauge; if it is below 1.0 bar, use the external filling loop to top it up to 1.5 barEnsure all radiator valves and underfloor heating zones are fully open to allow water to circulateRestart the boiler after adjusting the pressure to clear the temporary block

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