374 8C High

Worcester Bosch 374 8C Fault Code

Also written as 3748C — same fault.

The Worcester Bosch 374 8C fault code means: your boiler has detected repeated issues with maintaining its flame during operation, so it has locked itself for safety to ensure it does not attempt to fire incorrectly.. It appears on 2 Worcester Bosch models in our database.

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: Super-Lock caused by too frequent ionisation loss during burning
Typical repair cost £150-300 (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 374 8C fault code

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

Source

Worcester Bosch 374 8C 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 7 July 2026