High
343 ED on Worcester Bosch Greenstar CDi Compact

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.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

CH: flue gas temperature rising but supply temp. not

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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