How much does it cost to fix boiler error code F.86?

Typical repair cost for the boiler F.86 fault is £120-250 including labour.

F.86 Medium

Boiler Fault Code F.86

Also written as F86 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 7 July 2026

Fault code F.86 appears across 2 boiler brands and 26 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has detected that the connection to your underfloor heating system is interrupted or a safety sensor is not reporting correctly, so it has stopped providing heat to prevent damage. (As reported on Glow-worm Ultimate 3 25R)

Pick your boiler brand for the F.86 fix

Glow-worm F.86 17 models Vaillant F.86 9 models

Source

Information for the F.86 fault code is sourced from the official service / installation manual for each model that displays it. Read more about how we source fault codes →

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026