What does the Vaillant S.39 fault code mean?

Your boiler has paused because it has detected that an external safety switch for your underfloor heating has been triggered or disconnected.

How much does it cost to fix Vaillant error code S.39?

Typical repair cost for the Vaillant S.39 fault is £90-180 including labour.

Manufacturer manual

Underfloor heating contact open

From this model's manual

Verified against the Vaillant/Vaillant Home System installation & service manual, page 33.

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

Boiler cover options

A cover plan would handle faults like S.39: no call-out fees, no surprise bills.

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Seeing a different code? Every code this model can display, in one place.

Each noise points to a different fault.

Work through these before the call-out.

Safety-critical — turn off, read this.