Boiler Fault Code 8.iii

Also written as 8III — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026

Fault code 8.iii 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's water circulation system has become clogged with internal sludge or debris, making the pump struggle and create a grinding or rattling noise. (As reported on Chaffoteaux Celtic 2 24 Rsc)