A04
Hoval
Flue gas overtemperature
Furnace shuts down with flue gas temperature alarm, high flue temperature displayed
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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 gas path in Hoval flue heat exchanger, Undersized or obstructed chimney/flue system, Faulty flue gas temperature sensor, Incorrect burner adjustment causing high flue temperature
How to Fix / Troubleshooting
Safety: Switch off power and gas. Risk of flue gas spillage and burns. Allow flue components to cool.
- Inspect flue gas path: Remove the flue inspection cover on the Hoval furnace. Check for soot, debris, or collapsed baffles in the flue gas heat exchanger. Clean according to Hoval maintenance instructions.
- Check external flue: From a safe location, visually inspect the chimney or concentric flue for bird nests, ice, or other obstructions. Do not climb or work at height without proper equipment.
- Verify flue gas sensor: Locate the flue gas temperature sensor on the flue outlet. Check wiring for damage and ensure the sensor is firmly seated. Replace if the probe is deformed or heavily corroded.
- Reset and test: After cleaning and inspection, restore power and gas, then reset the alarm. Monitor flue gas temperature. If it quickly rises to alarm level again, a technician must check combustion settings and flue sizing.
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Repair Difficulty
Hard
4/5
Required Part
Flue Gas Temperature Sensor
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