i8 High

Boiler Fault Code i8

Also written as I8 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code i8 appears across 1 boiler brand and 1 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is failing to detect that you have turned on a hot tap, meaning it won't fire up to heat your water. (As reported on Sime Metropolis DGT 25 BF)

Pick your boiler brand for the i8 fix

Sime i8 1 model

Source

Information for the i8 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