Vaillant
Kettling / Boiling in Heat Exchanger
Water heater makes loud banging or knocking noises when heating water
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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 on primary heat exchanger, Low flow through heat exchanger, Air trapped in system, Incorrect gas rate causing local overheating
How to Fix / Troubleshooting
Safety: Switch off power and gas. Allow the unit to cool before touching the heat exchanger.
- Bleed air: Remove air from the primary circuit and heat exchanger using bleed points.
- Check flow: Ensure all valves are open and that the pump (if fitted) is operating correctly.
- Descale heat exchanger: Remove the primary or plate heat exchanger and descale using a suitable descaling solution, following Vaillant guidelines. In severe cases, replace the heat exchanger.
- Check gas rate (engineer): Verify that the burner is correctly adjusted to the rated input to avoid local boiling.
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Repair Difficulty
Hard
4/5
Required Part
Primary Heat Exchanger
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