Junkers
Heat exchanger kettling / localised boiling
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 heating circuit, Insufficient water flow due to partially blocked filter, Pump running at too low speed
How to Fix / Troubleshooting
Safety: No immediate gas hazard, but overheating risk exists. Turn down the flow temperature until the issue is resolved.
- Check system pressure: Ensure correct pressure to maintain good circulation.
- Bleed radiators: Remove trapped air that can cause hot spots.
- Clean system filter: If a Junkers or aftermarket magnetic filter is installed, isolate and clean it to restore flow.
- Technician actions:
- Power-flush or chemically clean the heating system to remove sludge and scale.
- Descale or replace the primary heat exchanger if heavily fouled.
- Adjust pump speed or replace the pump if underperforming.
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Repair Difficulty
Hard
4/5
Required Part
Primary Heat Exchanger
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