Boiler Fault Code 343 ED

Also written as 343ED — same fault.

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

Fault code 343 ED appears across 1 boiler brand and 2 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has detected that the exhaust gases are becoming dangerously hot while the water it is meant to be heating remains cold, forcing it to shut down to prevent damage or overheating. (As reported on Worcester Bosch Greenstar CDi Compact)