Medium
S.53 on Vaillant ecoTEC Plus 826

Your boiler has detected that water is not circulating properly through your radiators or pipes, and it has temporarily paused to prevent overheating.

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.

Technical description

Modulationblockedbyoperatingblockfunctionduetowaterdeficiency(flowandreturnspreadtoogreat)

DIY fix possible

Check your boiler's pressure gauge and top it up to 1.5 bar if it is below 1.0 bar using the filling key or loopEnsure all radiator valves are fully open to allow water to move freelyBleed your radiators using a radiator key to release any trapped air pockets

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Related fault codes

F.22View →F.23View →F.24View →

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