S.59 Medium

Vaillant S.59 Fault Code

Also written as S59 — same fault.

The Vaillant S.59 fault code means: your boiler is pausing because it cannot detect enough water flowing through the system to operate safely.. It appears on 2 Vaillant models 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: Waitingperiod:Minimumvolumeofcirculationwaternotachieved
Typical repair cost £120-250 (including labour)

DIY fix possible

Check that all radiator valves throughout your home are fully open.Check your system pressure gauge and top up to 1.5 bar if low.Ensure any external system pump or zone valves are powered on and functioning.

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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 31 August 2026