S.26 Low

Vaillant S.26 Fault Code

Also written as S26 — same fault.

The Vaillant S.26 fault code means: your boiler's internal cooling fan is staying on longer than expected after a heating cycle to ensure any remaining gases are cleared.. It appears on 35 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: Fan overrun

What causes the Vaillant S.26 fault?

This scenario occurs when the boiler's internal computer keeps the fan spinning after the burner has turned off to clear away residual heat and combustion gases. While it is often just a normal part of the cooling process, it can also happen if the system detects that temperatures inside the unit are staying high for longer than they should. In rare cases, it may indicate that the control board is misreading signals from the fan.

Typical repair cost £0-120 (including labour)

DIY fix possible

No action required; this is a status code, not a faultAllow the boiler to complete its cooling cycleMonitor only if the fan runs indefinitely without the boiler firing

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →

Vaillant models that show the S.26 fault code

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

Source

Vaillant S.26 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