E9 224
Worcester Bosch
Intermittent Overheat / Sensor Discrepancy
Boiler intermittently locks out with E9 224, often after running for some time.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Partially blocked primary heat exchanger, Air in system causing hot spots, Faulty overheat thermostat, Poor circulation due to partially blocked filter
How to Fix / Troubleshooting
Safety first: Allow the boiler and system to cool before bleeding or opening any components.
- Bleed air: Bleed radiators and any manual air vents on the system. Top up pressure to 1.0–1.5 bar afterwards.
- Clean filters: If a Worcester Bosch system filter or inline strainer is fitted, isolate and clean it thoroughly.
- Check pump speed: Ensure the pump is set to an appropriate speed for the system size (engineer may adjust settings on the pump or boiler menu).
- Engineer inspection: A professional should inspect the primary heat exchanger for scale or sludge, test the overheat thermostat, and consider a chemical flush if circulation is poor.
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Repair Difficulty
Hard
4/5
Required Part
Primary Heat Exchanger
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