S.16 High

Vaillant S.16 Fault Code

Also written as S16 — same fault.

The Vaillant S.16 fault code means: your boiler has detected an issue with the air fan system and has temporarily stopped heating to prevent further damage.. It appears on 40 Vaillant models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: DHW mode: Fan overrun

What causes the Vaillant S.16 fault?

This fault occurs when the boiler's control system detects that the fan is spinning but sending back incorrect signals, or it isn't spinning at the speed required for safe combustion. The most common reason is an internal electrical failure within the fan motor itself or a communication glitch between the fan and the main circuit board. Without the fan functioning perfectly to clear exhaust gases, the boiler shuts down as a safety precaution.

Typical repair cost £250-480 (including labour)

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.16 fault code

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

Source

Vaillant S.16 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