Immergas
Kettling / Localised Boiling in Heat Exchanger
Boiler makes loud banging or knocking noises (kettling) during operation, especially at high temperature.
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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
Limescale build-up in primary heat exchanger, Sludge in system water, Low flow rate through boiler, Incorrect pump speed setting
How to Fix / Troubleshooting
Safety: No immediate danger if the boiler is not leaking, but prolonged kettling can damage the heat exchanger. Allow the boiler to cool before working on it.
- Check system flow: Ensure all radiator valves are sufficiently open and that bypass valves (if fitted) are correctly set.
- Adjust pump speed: On models with adjustable pumps, set the pump to a higher speed to increase flow through the heat exchanger.
- System cleaning (engineer): A professional should dose the system with a suitable cleaner and flush to remove sludge and scale. In hard water areas, a chemical descaling of the primary heat exchanger may be required.
- Inhibitor: After cleaning, add a corrosion inhibitor to the system to prevent future build-up.
- Monitor: Run the boiler and listen for reduction in noise. Persistent kettling may require heat exchanger replacement.
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Repair Difficulty
Hard
4/5
Required Part
Primary Heat Exchanger
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