Saunier Duval
Kettling / Localised Boiling in Heat Exchanger
Boiler makes loud banging or kettling noises during operation
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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 central heating system, Poor circulation due to failing pump, Incorrect system pressure
How to Fix / Troubleshooting
Safety first: If noises are very loud or the boiler vibrates excessively, switch it off and allow it to cool.
Steps to check:
- Check system pressure and top up to the recommended level (around 1.2–1.5 bar cold).
- Bleed radiators to remove trapped air that can worsen kettling.
- Ensure all radiator valves are open to allow good circulation.
- Listen to the pump; if it is noisy or very hot, it may not be circulating properly.
- Arrange for a professional to chemically clean or power flush the system and, if necessary, descale or replace the primary heat exchanger.
Warning: Persistent kettling can damage the heat exchanger and should not be ignored.
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Repair Difficulty
Hard
4/5
Required Part
Primary Heat Exchanger
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