Boiler Fault Code 8.6

Also written as 86 — same fault.

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

Fault code 8.6 appears across 3 boiler brands and 6 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is vibrating or making unusual banging or whistling noises while running, which often indicates trapped air in the system or a build-up of internal debris. (As reported on Glow-worm Space Saver 30 40 50)