BoilerFaultCodesWorcester Bosch 305 Fault Code
The Worcester Bosch 305 fault code means: your boiler is temporarily pausing the hot water production to prevent itself from overheating or cycling on and off too frequently.. It appears on 13 Worcester Bosch models in our database.
Technical description: Boiler in hot water anti-cycle mode
What causes the Worcester Bosch 305 fault?
This code appears when the boiler has reached its maximum internal temperature for hot water and needs to briefly shut down the burner to cool down. It is often caused by a lack of water flow through the heat exchanger, or because the taps have been turned on and off very quickly several times. By entering this mode, the boiler is simply protecting its internal components from excessive heat and wear.
This can be slightly more common in summer, as the incoming mains water is naturally warmer and the boiler reaches its target temperature much faster than in the winter.
DIY fix possible
Wait up to 15 minutes for the anti-cycle timer to expireEnsure hot water taps are fully closedCheck that the hot water temperature setting on the control panel is not set excessively high
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Worcester Bosch models that show the 305 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 305 fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.
- Worcester Bosch 24/28/35 CDi MkII manual (PDF)
- Worcester Bosch Greenstar 1000 manual (PDF)
- Worcester Bosch Greenstar 12i System manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026