S.59 Medium

Vaillant S.59 Fault Code

Also written as S59 — same fault.

The Vaillant S.59 fault code means: your boiler is temporarily pausing because it cannot detect enough water flowing through the system to heat it safely.. It appears on 1 Vaillant model in our database.

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.

Technical description: Waiting time: Water circulation vol. (Minimum circulation water volume)
Typical repair cost £100-250 (including labour)

DIY fix possible

Check that all radiator valves throughout your home are fully openEnsure your system pressure is at the correct level, typically between 1.0 and 1.5 barCheck for any blockages in your external magnetic system filter if one is fitted

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Vaillant models that show the S.59 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Vaillant S.59 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026