E08
NTI
Flue Gas Temperature Sensor Fault / Overtemperature
Boiler shows E08 and stops; flue temperature reading is abnormally high or low
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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 sensor, Loose sensor connection, Blocked heat exchanger or flue, Incorrect combustion causing high flue temps
How to Fix / Troubleshooting
Safety: High flue temperatures can damage venting and create fire risk. Turn off power and gas before inspection.
- Check flue sensor: Locate the flue gas NTC sensor on the exhaust outlet or flue collar. Inspect for damage or soot buildup. Clean gently and ensure it is firmly mounted.
- Inspect wiring: Verify the sensor harness is intact and fully seated at the control board.
- Test resistance: Measure sensor resistance and compare to NTI specifications. Replace if out of range.
- Check for restrictions: Examine the flue and intake for blockages and the heat exchanger for heavy scale or soot. A technician should perform a combustion analysis and clean the heat exchanger if needed.
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Repair Difficulty
Hard
4/5
Required Part
Flue Gas Temperature Sensor
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