E5
Junkers
Flue gas overtemperature / flue NTC fault
Boiler displays E5; flue gas temperature too high or sensor fault
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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
Blocked flue or condensate trap, Defective flue gas NTC, Sooted or scaled heat exchanger, Fan speed too low
How to Fix / Troubleshooting
Safety: Switch off the boiler and do not operate it until the flue system has been checked. Risk of flue gas spillage.
- External inspection: Check the flue terminal for obstructions and clear them.
- Condensate trap: Ensure the condensate drain from the Junkers condensing boiler is not blocked or frozen; thaw and clear as needed.
- Technician actions:
- Inspect and clean the primary heat exchanger and flue ways.
- Check flue gas NTC resistance and replace if out of specification.
- Verify fan speed and operation.
- Confirm that the flue system is correctly installed and not restricted.
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Repair Difficulty
Professional Required
5/5
Required Part
Flue Gas Temperature Sensor (NTC)
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