York Combustion / Venting Hazard

Furnace runs but carbon monoxide detector alarms when heating.

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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

Cracked heat exchanger, Blocked flue, Improper combustion air, Backdrafting into living space

How to Fix / Troubleshooting

Life safety: Treat any CO alarm as an emergency.

  • Shut down furnace: Turn off power and gas to the furnace immediately.
  • Evacuate: Leave the building and call emergency services or the gas utility from outside.
  • Do not restart: Do not operate the furnace again until a qualified HVAC technician has inspected the heat exchanger, venting, and combustion.
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Repair Difficulty

Professional Required 5/5

Required Part

Heat Exchanger
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