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

Typical repair cost for the boiler 321 fault is £120-220 including labour.

321 Medium

Boiler Fault Code 321

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 7 July 2026

Fault code 321 appears across 5 boiler brands and 25 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is currently unable to monitor the temperature of your hot water properly, so it has safely shut down the hot water function to prevent overheating. (As reported on ECA FELiS FL 50 HM)

Pick your boiler brand for the 321 fix

Baxi 321 13 models ECA 321 1 model Main 321 3 models Potterton 321 4 models Worcester Bosch 321 4 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 7 July 2026