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.

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.

Comfort protection mode for the heat cell

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Each noise points to a different fault.

Sludge build-up — needs flushing, not bleeding.

Safety-critical — turn off, read this.