How much does it cost to fix Worcester Bosch error code 343 ED?

Typical repair cost for the Worcester Bosch 343 ED fault is £180-350 including labour.

343 ED High

Worcester Bosch 343 ED Fault Code

Q: What does the Worcester Bosch 343 ED fault code mean?

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.

Also written as 343ED — same fault.

The Worcester Bosch 343 ED fault code means: 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.. It appears on 2 Worcester Bosch models in our database.

Technical description: CH: flue gas temperature rising but supply temp. not

Typical repair cost £180-350 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Worcester Bosch models that show the 343 ED fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Worcester Bosch 343 ED fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.

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