How much does it cost to fix Vaillant error code S.56?

Typical repair cost for the Vaillant S.56 fault is £150-300 including labour.

S.56 Emergency

Vaillant S.56 Fault Code

Q: What does the Vaillant S.56 fault code mean?

Your boiler has detected high levels of carbon monoxide and has automatically paused operation to keep you safe while it waits for the fumes to clear.

Also written as S56 — same fault.

The Vaillant S.56 fault code means: your boiler has detected high levels of carbon monoxide and has automatically paused operation to keep you safe while it waits for the fumes to clear.. It appears on 1 Vaillant model in our database.

Technical description: Waitingtime:COlimitvalueexceedance | Waitingperiod:COlimitvalueexceedance

Typical repair cost £150-300 (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.56 fault code

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

ecoTEC exclusive Repair: £150-300

Source

Vaillant S.56 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