A08
De Dietrich
Flue Gas Temperature Too High
Boiler shows A08 and stops, often after a few minutes of 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
Partially blocked flue, scaled or dirty primary heat exchanger, faulty flue gas temperature sensor, incorrect gas rate
How to Fix / Troubleshooting
Safety: High flue temperature can indicate dangerous combustion. Do not bypass or reset repeatedly without finding the cause.
- Check flue outlet: Ensure the terminal is clear and that any flue extensions are properly supported and not crushed.
- System flow: Verify that all radiators/underfloor zones are open and that circulation is adequate. Poor heat removal can overheat flue gases.
- Technician tasks: A heating engineer should clean the primary heat exchanger, check the flue gas temperature sensor, and verify combustion with an analyser. Replace the sensor or adjust gas valve as required.
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Repair Difficulty
Professional Required
5/5
Required Part
Flue Gas Temperature Sensor
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