BoilerFaultCodesWorcester Bosch 224 Fault Code
The Worcester Bosch 224 fault code means: your boiler has shut down because a safety sensor has detected that it is getting far too hot, likely due to a blockage or a pump failure.. It appears on 9 Worcester Bosch models in our database.
Technical description: Maximal flue gas thermostat or heat exchanger maximal thermostat has activated
What causes the Worcester Bosch 224 fault?
This fault occurs when the water inside the boiler reaches an unsafe temperature or the flue gases become too hot, triggering a safety shut-off to prevent damage. The most common reasons are a failed internal pump that isn't moving water away quickly enough or a blockage in the system from sludge and debris. It can also be caused by an air lock or a closed valve stopping the flow of water through the heat exchanger.
This fault is more common in autumn when heating systems are switched back on after a long summer break, as pumps are prone to seizing during periods of inactivity.
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 224 fault code
Click a model for the full fault code list and model-specific repair notes.
- 24/28/35 CDi MkII Repair: £150-300
- Greenstar 1000 Repair: £120-250
- Greenstar 12i System Repair: £150-300
- Greenstar 2000 Repair: £150-300
- Greenstar 27CDi Repair: £150-300
- Greenstar 28CDi Repair: £150-300
- Greenstar 4000 Repair: £150-350
- Greenstar 8000 Life & Style Repair: £120-£350
- Greenstar CDi Compact Repair: £150-300
Source
Worcester Bosch 224 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