How much does it cost to fix Vaillant error code S.1?

Typical repair cost for the Vaillant S.1 fault is £150-£450 including labour.

S.1 High

Vaillant S.1 Fault Code

Q: What does the Vaillant S.1 fault code mean?

Your boiler is preparing to ignite but is stuck at the stage where the internal fan is spinning up to clear the combustion chamber.

Also written as S1 — same fault.

The Vaillant S.1 fault code means: your boiler is preparing to ignite but is stuck at the stage where the internal fan is spinning up to clear the combustion chamber.. It appears on 26 Vaillant models in our database.

Technical description: Fan running

What causes the Vaillant S.1 fault?

This status occurs when the boiler is attempting to start its ignition sequence but becomes stuck while the fan is spinning. It typically happens because the fan cannot reach the required speed or the boiler's control board fails to receive a signal confirming that the fan is working correctly. This prevents the boiler from safely moving to the next stage of lighting the burner.

Typical repair cost £150-£450 (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.1 fault code

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

Source

Vaillant S.1 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