S.14 Low

Vaillant S.14 Fault Code

Also written as S14 — same fault.

The Vaillant S.14 fault code means: your boiler is operating normally and has successfully lit the flame to heat your water or radiators.. It appears on 37 Vaillant models in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Burner ignited

What causes the Vaillant S.14 fault?

This fault occurs when the boiler's internal flow sensor incorrectly detects that water is running through the hot water pipes, even when all your taps are closed. The most common reason is a sticking internal component or a faulty sensor that is sending a false signal to the boiler's brain. Because the boiler thinks you are prioritising a hot bath or shower, it refuses to switch over to provide heat for your radiators.

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Vaillant models that show the S.14 fault code

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

Source

Vaillant S.14 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 7 July 2026