12
Immergas
Primary Circuit Overheat / Limit Thermostat Intervention
Furnace shows 12, burner shuts down, may be accompanied by loud boiling noises
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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
Scale buildup in primary heat exchanger, Insufficient circulation due to weak pump, Air in system, Closed valves or blocked filters
How to Fix / Troubleshooting
Safety: Overheating can cause very hot surfaces and water. Turn off power and allow the unit to cool before touching any components.
Steps:
- 1. Check system pressure and bleed air: Ensure pressure is correct and bleed radiators to remove air pockets.
- 2. Verify all valves are open: Confirm that isolation valves under the boiler and radiator valves are open.
- 3. Listen to pump: When the boiler calls for heat, you should hear or feel the circulation pump running. If it is silent or very hot to the touch, it may be seized.
- 4. Clean system filter: If your Immergas installation includes a return filter or magnetic filter, isolate and clean it to restore flow.
- 5. Technician tasks: Descale or replace the primary heat exchanger if heavily fouled, and replace the pump if it is not delivering adequate flow.
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Repair Difficulty
Hard
4/5
Required Part
Primary Heat Exchanger
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