How much does it cost to fix Vaillant error code S.61?

Typical repair cost for the Vaillant S.61 fault is £150-£450 including labour.

S.61 High

Vaillant S.61 Fault Code

Q: What does the Vaillant S.61 fault code mean?

Your boiler has failed a safety check during its start-up sequence because it cannot identify the gas type or verify the flame correctly.

Also written as S61 — same fault.

The Vaillant S.61 fault code means: your boiler has failed a safety check during its start-up sequence because it cannot identify the gas type or verify the flame correctly.. It appears on 7 Vaillant models in our database.

Technical description: Gas family check unsuccessful

What causes the Vaillant S.61 fault?

This fault occurs when the boiler's internal computer tries to verify the quality and type of gas entering the system but fails to receive a stable reading. It is physically caused by a mismatch between the gas valve's output and the detection signal from the ignition probes, often due to a components failing to regulate the fuel flow correctly. The most common reason is a malfunctioning gas valve or a faulty control board that can no longer process the flame signal.

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.61 fault code

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

Source

Vaillant S.61 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