How much does it cost to fix Worcester Bosch error code 6b?

Typical repair cost for the Worcester Bosch 6b fault is £120-£250 including labour.

6b High

Worcester Bosch 6b Fault Code

Q: What does the Worcester Bosch 6b fault code mean?

Your boiler has shut down because it detected that the exhaust gases are getting too hot, which is a safety mechanism to prevent damage to the flue system.

Also written as 6B — same fault.

The Worcester Bosch 6b fault code means: your boiler has shut down because it detected that the exhaust gases are getting too hot, which is a safety mechanism to prevent damage to the flue system.. It appears on 1 Worcester Bosch model in our database.

Technical description: Type b Flue overheat thermostat (Grommet type)

Typical repair cost £120-£250 (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 6b fault code

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

Greenstar i Junior Repair: £120-£250

Source

Worcester Bosch 6b 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