Baxi
Kettling / Localised Boiling in Heat Exchanger
Boiler makes loud banging or knocking noises (kettling) when heating is on
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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 Baxi primary heat exchanger, Sludge restricting flow, Pump running too slowly, Incorrect system balancing causing poor circulation
How to Fix / Troubleshooting
Safety first: Persistent kettling can damage the boiler. Do not ignore loud banging.
User checks:
- Ensure all or most radiator valves are open to allow good flow.
- Bleed radiators to remove trapped air and top up system pressure afterwards.
- Check that the pressure is around 1.2–1.5 bar when cold.
Professional actions:
- A heating engineer may dose the system with a descaling or cleaning chemical, flush the system, and clean or replace the primary heat exchanger if heavily scaled.
- They will also check pump speed and system balancing.
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Repair Difficulty
Medium
3/5
Required Part
Primary Heat Exchanger
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