Carbon Monoxide Alarm Going Off When the Furnace Is On in Arlington, TX

If your carbon monoxide alarm is going off when the furnace is on in Arlington, leave. This is not a filter check, a thermostat check, or a reset. Get everyone out of the house now, including pets. Call 911 from outside. You can also call the gas utility from outside. Do not reset the alarm and keep the furnace running.

Carbon monoxide has no smell. A furnace that seems to be heating normally can still be putting it into the house. Headache, nausea, dizziness, confusion, or flu-like symptoms that ease outdoors are reasons to get out even if you have not found the alarm yet. Do not stay to see if the feeling passes.

The steps below are the whole job until you are outside and help is coming. The explanation of furnaces comes after that, for when the house has been cleared. It is not something to read in the hallway while the alarm is sounding.

Get out, then call

Do these in order.

1. Get everyone out, including children, anyone who was asleep, and pets. Do not split up to "just check the furnace."
2. Do not open windows and stay inside to air the house out. Fresh air is outside, with the door closed behind you.
3. Do not reset the alarm, silence it, and go back to the couch. Silencing it does not stop the furnace.
4. From outside, call 911. Tell them a carbon monoxide alarm sounded and the furnace was on. If someone feels sick, say so. You can also call the gas utility from outside. If you smell gas, a rotten egg odor, say that too.
5. Do not go back in for a phone, keys, or to flip the furnace switch. If a switch is literally on your way out the door, you may turn the furnace off as you leave. Do not return for it.
6. Wait for the fire department or the gas utility. They decide when the air is safe to re-enter. Feeling better in the driveway is not that decision. Move farther from the house if the alarm was loud at the door or anyone is ill. Fresh air helps. It is not a treatment you manage yourself. EMS makes that call.

A neighbor's house is a fine place to wait. So is the yard, if everyone is far enough from the door and accounted for. Do not send one person back in to start opening windows.

After the house is cleared, the furnace stays off

The fire department or the gas utility can clear the air and tell you it is safe to go back inside. That visit does not repair a heat exchanger, reseat a flue, or sign the furnace back on. A cleared house with the same furnace running again is how the alarm happens a second time.

Leave the furnace off until a technician has checked it. Use another heat source only if it is designed for indoor use and is not a generator, a grill, or a fuel heater in the garage or the house. Those make carbon monoxide too. If you cannot safely heat another way, that is a reason to stay elsewhere until the furnace is checked, not a reason to reset the alarm.

Space heaters that plug in still need a sound cord and a clear space around them. They are a stopgap. They are not a cracked heat exchanger.

Why a furnace can set the alarm off

Read this after you are safe, or before the season, not during an alarm.

Carbon monoxide comes from incomplete combustion. A gas furnace is supposed to send those products out the flue. The alarm means some of them are in the rooms, or the alarm believes they are. Either way, the furnace stays off until someone measures it.

Causes a technician looks for:

• A cracked or rusted heat exchanger. Combustion products cross into the air the blower pushes through the ducts. This is not a cleaning. It is not a part you reset. A failed heat exchanger ends the repair on that furnace. Leave it off.
• A blocked flue. A nest, a collapsed liner, a cover left on a PVC pipe, or a metal flue that has come apart. High-efficiency furnaces use plastic intake and exhaust. From the ground, those pipes should be clear. Do not climb into the attic during an alarm, and do not climb later to shove a pipe back together and call it fixed.
• A failed inducer or pressure switch. The furnace is supposed to prove it can exhaust before the gas valve opens. A unit that fires without that proof, or a vent that leaks after the inducer, can spill combustion products. Homeowners do not jumper those switches.
• Backdrafting. Bath fans, a kitchen hood, a dryer, and a tight house can pull exhaust back down a weak flue. A water heater that shares a vent with the furnace can be part of that. The fix is the venting and the air supply, not a longer shower of "airing it out."
• Intake and exhaust too close, or recirculating. On a condensing furnace, exhaust can be pulled back into the intake if the pipes were terminated wrong or something is blocking one of them. The furnace then burns its own exhaust. That is an install problem, and it stays off until it is corrected.

A dusty burning smell on the first cold night is a different article. It does not mean the air is free of carbon monoxide, and it does not mean an alarm is dust. Furnace burning smell on first startup in Arlington is only for a light dusty smell you are watching, with no alarm and no symptoms. Furnace smells like burning in Garland is the worry list for odors. Weird smell when the furnace turns on in Irving sorts smells that are not an alarm. If the alarm is sounding, you are done with smell guides. You are outside.

What not to do

• Do not pull the burner cover to look at the flame while the alarm is going, or after you have gone back in against instructions.
• Do not tape a flue, wire a rollout switch closed, or bypass a pressure switch so the furnace will run.
• Do not relight a pilot.
• Do not assume the alarm is "sensitive" because it happened once and then stopped. Stopping can mean the furnace cycled off. The next cycle can bring it back.
• Do not run the furnace "to see" after you replace the alarm battery. A new battery in an alarm that just went off is not a repair.

Soot at a register, a yellow lazy flame you can see through the sight glass, or rust flakes around the burner opening are reasons the furnace was already unsafe, even on a day the alarm has not sounded. Shut it off and call. Do not remove the cover to get a better look.

Chirps, batteries, and alarms that are not this emergency

Learn this on a calm afternoon.

A real alarm is a loud, continuous horn, or the pattern printed on that detector. That pattern means leave. It does not mean hunt for a battery.

A single chirp every so often, with no alarm, is often a low battery or a detector that has reached the end of its life. Many carbon monoxide alarms expire in about 5 to 7 years, and some last up to about 10. The date is on the back. Replace the unit when it expires. A fresh battery in an expired alarm is not a working alarm.

Put a carbon monoxide alarm on each floor, and outside sleeping rooms, following the manufacturer's placement. Test them monthly when everyone feels well. A test chirp during a monthly test is not an emergency. An alarm you did not start is.

If you are ever unsure whether you are hearing a chirp or an alarm, treat it as an alarm and leave. You can be wrong in the driveway. You do not want to be wrong in a bedroom.

What the technician does

Furnace repair after a carbon monoxide alarm is a combustion and heat-exchanger visit, not a filter visit.

The technician should measure carbon monoxide in the flue and be prepared to measure it in the supply air, inspect the heat exchanger as far as that furnace allows, check the vent draft and the pipe joints, and confirm the inducer and safety switches actually work. A cracked heat exchanger means the furnace stays off and the conversation turns to replacement. Sizing, ductwork, airflow, the vent, and the permit matter more on that replacement than the brand. If the cooling coil is opened as part of the job, the refrigerant charge has to be done correctly too. You should hear the finding and the price before parts are sold, and you should not be talked into running the old furnace "until the new one arrives" if the exchanger is failed.

HVAC service in Arlington is the local page for that visit, after the emergency is over.

After everyone is safe

Boost Air And Plumbing repairs gas furnaces in Arlington, Grand Prairie, Mansfield, Fort Worth, and nearby communities. If the heat exchanger has failed, ask for a replacement estimate. Free estimates, no pressure. Do not call us instead of 911 while the alarm is sounding. Call 911 from outside first.

See our furnace repair service and HVAC service in Arlington. Call (817) 612-9107 or book online. Hours are Monday through Saturday, 8am to 7pm, with after-hours and Sunday emergency appointments available.

Frequently asked questions

What should I do if the carbon monoxide alarm goes off when the furnace is on? Get everyone out now, including pets. Do not look for the source, open windows and stay inside, or reset the alarm and keep the furnace running. From outside, call 911. You can also call the gas utility from outside. Do not go back in for a phone, a wallet, or to turn the furnace off. Wait until the fire department or the gas utility says the house is clear.

Is a carbon monoxide alarm a false alarm if I feel fine? Do not decide that from inside the house. Carbon monoxide has no smell, and people can have it in their blood before they feel very sick. A sounding alarm means leave and call 911 from outside. Feeling fine is not a test. The fire department or EMS decides when it is safe to go back in.

Can I reset the alarm and run the furnace if it stops? No. Resetting the alarm and leaving the furnace on is how people go back to sleep with the same problem. After everyone is outside and 911 has been called, leave the furnace off. A house the fire department has aired out is not a repaired furnace. The heat exchanger and the vent still have to be checked before anyone heats with it again.

Why would the furnace set off a carbon monoxide alarm? Common causes are a cracked heat exchanger, a blocked or disconnected flue, a failed inducer, exhaust pulled back into the house, or intake and exhaust pipes that are blocked or too close together on a high-efficiency furnace. A water heater on a shared vent can backdraft at the same time. None of those are a filter change. The furnace stays off until a technician checks combustion and the heat exchanger.

What is the difference between a chirp and an alarm? A continuous alarm, or the pattern your alarm's manual calls an alarm, means leave the house. A single chirp every minute or so, with no alarm horn, is often a low battery or an expired detector. You sort that out when nobody is ill and no alarm is sounding. You do not change a battery while an alarm is going off, and you do not treat a real alarm as a battery.