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Shut the furnace off: possible cracked heat exchanger
Short cycling with soot or a burning or metallic smell can point to a cracked heat exchanger. Shut the furnace off and call an HVAC technician today.
Why this happens
Lennox lists soot around the burners or vents, a burning, metallic or chemical odor, frequent short cycling and rust as signs of a cracked heat exchanger. Carrier warns that a cracked heat exchanger can leak carbon monoxide. Lennox's advice is to shut off the furnace, ventilate your home, and contact an HVAC professional.
What to do right now
- Set the thermostat to Off, then turn off the furnace's power switch.
- Open windows to ventilate the house, as Lennox advises.
- If a CO alarm sounds or anyone feels headachy, dizzy or sick, get everyone outside and call 911.
- Call an HVAC technician and don't run the furnace until it has been inspected.
- Don't open the furnace or try to clean the soot.
What to tell the HVAC technician
- What you saw or smelled, and where: soot, rust, a burning, metallic or chemical odor.
- How long each heating cycle lasted before it shut off.
- Whether any CO alarm has gone off, even briefly.
- The brand, model, serial and approximate age of the furnace.
Build the full list: what to tell the HVAC technician.
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References (every fact above comes from one of these pages)
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