How much does it cost to fix boiler error code 321?

Typical repair cost for the boiler 321 fault is £150-300 including labour.

321 High

Boiler Fault Code 321

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 27 April 2026

Fault code 321 appears across 2 boiler brands 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 internal computer is unable to talk to its control panel, meaning the system has safely shut down to prevent incorrect operation. (As reported on Main Insul 7)

Pick your boiler brand for the 321 fix

Main 321 1 model Worcester Bosch 321 2 models

Source

Information for the 321 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