Vent, Valve & Volt
Carbon monoxide alarm going off or beeping

This one needs a licensed pro

Responders cleared it: have the source checked

A cleared home still needs its cause found. Call a qualified technician to inspect the fuel-burning appliances, and leave again if the alarm sounds.

Why this happens

NFPA says to stay out until emergency personnel say it is safe to go back in. Nest says to stay out until the responders arrive, the home has been aired out and the alarm is back to normal, and adds that if the alarm sounds again within 24 hours you go through the leave and call steps again and call a qualified appliance technician to look for CO sources. EPA says to have a qualified technician inspect fuel-burning appliances and chimneys and check that nothing blocks the fumes from venting outside. CDC says to have the heating system, water heater and other gas, oil or coal appliances serviced yearly by a qualified technician.

What to do right now

  1. Go back in only when responders say it is safe, and follow what they tell you about which appliances to leave off.
  2. Ask what they found and write it down. If your alarm shows a peak reading, write that down too. Nest says the peak level its Protect alarm records can help a fire safety professional or technician find the source.
  3. Call a qualified technician to inspect your fuel-burning appliances and chimney or flue. For a furnace, that is an HVAC technician. For a gas water heater, that is a licensed plumber or gas appliance technician, and for a chimney or flue, a chimney sweep or inspector.
  4. Do not open, adjust or try to repair a furnace, water heater or other appliance yourself.
  5. Never run a car in a garage attached to the house, even with the door open. CPSC says to run a generator only outside, at least 20 feet from the home, with the exhaust facing away.
  6. If the alarm sounds again, leave and call 911 again.

When to stop. If the alarm sounds again, or anyone feels unwell, leave at once and call 911.

What to tell the HVAC technician

  • What the responders found and any reading they gave you.
  • Which alarm sounded, when, and its peak reading if it shows one.
  • Which fuel-burning appliances you have, and when each was last serviced.
  • Whether a vehicle, generator or grill was running near the home.

Build the full list: what to tell the HVAC technician.

Related troubleshooters

Start this troubleshooter over

References (every fact above comes from one of these pages)
  1. EPA: Protect your family and yourself from carbon monoxide poisoning
  2. CDC: Carbon monoxide poisoning basics
  3. CPSC: Carbon monoxide
  4. NFPA: Educational messages desk reference, chapter 3, carbon monoxide (PDF)
  5. Google Nest Help: What to do if carbon monoxide is detected
  6. Google Nest Help: Learn about carbon monoxide (CO)

FourHome is our sister brand. Browse all FourHome replacement faucet and shower parts on the FourHome Amazon store. We earn from purchases made through this link.