Vaillant
Boiler Kettling / Localized Boiling in Heat Exchanger
Loud banging or knocking noises (kettling) from Vaillant boiler 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 buildup in primary heat exchanger, Sludge in system reducing flow, Pump running at too low speed, Incorrect system balancing causing low flow through boiler
How to Fix / Troubleshooting
Safety: No immediate danger if sealed, but turn down the thermostat and allow the boiler to cool if noises are severe.
User actions:
- Ensure all radiator valves are open to allow adequate flow.
- Check system pressure and top up if low.
Professional actions:
- Powerflush or chemically clean the heating system to remove sludge.
- Descale or replace the primary heat exchanger if heavily scaled (common in hard water areas without inhibitor).
- Check pump speed settings and system balancing.
Ignoring kettling can shorten heat exchanger life.
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Repair Difficulty
Hard
4/5
Required Part
Primary Heat Exchanger
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