How much does it cost to fix Vaillant error code S.86?

Typical repair cost for the Vaillant S.86 fault is £150-350 including labour.

S.86 High

Vaillant S.86 Fault Code

Q: What does the Vaillant S.86 fault code mean?

Your boiler has detected an issue with its internal combustion chamber and has entered a protective standby mode to prevent damage.

Also written as S86 — same fault.

The Vaillant S.86 fault code means: your boiler has detected an issue with its internal combustion chamber and has entered a protective standby mode to prevent damage.. It appears on 1 Vaillant model in our database.

Technical description: Comfort protection mode for the heat cell

Typical repair cost £150-350 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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.86 fault code

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

ecoTEC exclusive Repair: £150-350

Source

Vaillant S.86 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