F25
Saunier Duval Flue Gas Recirculation / CO Protection

Furnace displays F25, burner shuts down, may be associated with flue gas recirculation

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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

Incorrect flue installation,Blocked or damaged flue terminal,Strong wind causing flue gas blowback,Defective flue gas sensor

How to Fix / Troubleshooting

Critical safety warning: F25 can indicate dangerous flue gas conditions. Do not operate the furnace until the flue system has been checked by a qualified technician.

  • Visual flue check: From outside, ensure the flue terminal is correctly positioned and unobstructed. Look for signs of damage or incorrect proximity to openings.
  • Check surroundings: Remove any objects near the flue terminal that could cause recirculation of exhaust gases.
  • Sensor inspection: A technician should inspect and test the flue gas sensor and replace it if faulty.
  • Flue system inspection: Have a certified professional inspect the entire flue for compliance, integrity, and correct routing.
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Repair Difficulty

Professional Required 5/5

Required Part

Flue Gas Sensor
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