BoilerFaultCodesWorcester Bosch 604 Fault Code
The Worcester Bosch 604 fault code means: your boiler has stopped working because its internal computer has detected a communication error with the burner control system.. It appears on 7 Worcester Bosch models in our database.
Technical description: System fault burner control unit
What causes the Worcester Bosch 604 fault?
This fault occurs when the boiler's main control centre loses its ability to 'talk' to the components that manage the gas burner. It is typically caused by a physical break in the internal wiring or a critical failure within the printed circuit board itself, preventing the boiler from firing safely. Essentially, the boiler has shut down because its internal systems can no longer coordinate the ignition process.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Worcester Bosch models that show the 604 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 604 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