This one needs a licensed pro
Blocked vent pipe: shut the furnace off and call a technician
A blocked furnace vent can push exhaust back into the house. Turn the furnace off and call an HVAC technician now.
Why this happens
Bryant lists blocked exhaust among the causes of short cycling, and Trane warns that a blocked flue creates a risk of carbon monoxide poisoning. Bryant says not to attempt to repair or modify furnace venting yourself. The CPSC recommends a yearly professional inspection of all fuel-burning heating systems, including flues and vents.
What to do right now
- Set the thermostat to Off, then turn off the furnace's power switch.
- Don't clear, cut, move or modify the vent pipe yourself.
- If a CO alarm sounds or anyone feels headachy, dizzy or sick, get everyone outside and call 911.
- Call an HVAC technician and leave the furnace off until it has been checked.
What to tell the HVAC technician
- What is blocking the vent pipe and where it exits the house. A photo helps.
- How long each heating cycle lasted.
- Whether any CO alarm has gone off.
- The brand, model and serial from the furnace's data plate.
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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