Medium
F.86 on Vaillant Home Combi

Your boiler has detected that the external safety switch for your underfloor heating system is reporting a fault, so it has shut down to prevent potential overheating or damage.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

What the manual says

Manufacturer manual

Fault: Underfloor heating contact

From this model's manual
Verified against the Vaillant Home Combi installation & service manual, page 36.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

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

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