BoilerFaultCodes 8.ii High
Boiler Fault Code 8.ii
Also written as 8II — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 8.ii appears across 1 boiler brand and 3 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler is struggling because trapped air is preventing water from circulating properly, which is making the pump sound noisy and preventing heating. (As reported on Chaffoteaux Celtic 2 24 Rsc)
Pick your boiler brand for the 8.ii fix
Source
Information for the 8.ii 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 27 April 2026