E12
Attack
Flue Gas Temperature Sensor / Safety Device Fault
Boiler displays E12 and stops; may be associated with flue gas sensor or safety device.
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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
Failed flue gas temperature sensor on Attack condensing boiler, Overheated flue due to blocked heat exchanger, Loose or damaged sensor wiring, Faulty main PCB
How to Fix / Troubleshooting
Safety: Risk of flue gas overheating. Turn off the boiler and do not operate until the cause is identified.
Steps:
- Check flue outlet: Ensure the external flue terminal is not blocked.
- Inspect flue sensor: Locate the flue gas temperature sensor on the flue outlet or near the heat exchanger. Check for secure mounting and intact wiring.
- Clean heat exchanger: A heavily fouled heat exchanger can cause high flue temperatures. Have the primary and condensing sections cleaned according to Attack service instructions.
Professional service: Flue gas safety components should be tested and replaced only by qualified personnel.
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Repair Difficulty
Hard
4/5
Required Part
Flue Gas Temperature Sensor
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