How much does it cost to fix boiler error code i21?

Typical repair cost for the boiler i21 fault is £120-250 including labour.

i21 High

Boiler Fault Code i21

Also written as I21 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 27 April 2026

Fault code i21 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 displaying its internal software version, which indicates a configuration error rather than a physical part failure. (As reported on Worcester Bosch Greenstar Heatslave II)

Pick your boiler brand for the i21 fix

Worcester Bosch i21 1 model

Source

Information for the i21 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