Alpha
Kettling Due to Scale or Sludge
Boiler makes loud banging or knocking noises (kettling) 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 on primary heat exchanger, Sludge in system water, Restricted circulation, Incorrect pump speed setting
How to Fix / Troubleshooting
Safety: Allow the boiler to cool before touching any components.
- Check system pressure: Ensure the pressure is within the recommended range (1.0–1.5 bar cold). Low pressure can worsen kettling.
- Bleed radiators: Remove trapped air from radiators to improve circulation.
- Clean system filter: If an Alpha magnetic filter is installed, isolate and clean it to remove sludge.
- Chemical treatment (qualified person): A heating engineer can add a system cleaner, run the system, then flush and refill with inhibitor to reduce kettling.
- Descale heat exchanger: In hard water areas, the primary heat exchanger may need descaling or replacement.
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Repair Difficulty
Hard
4/5
Required Part
Primary Heat Exchanger
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