Furnace quit on you? Before you call anyone, try the easy stuff. Make sure the thermostat’s set to heat. Swap the filter if it’s dirty. Reset the breaker and the furnace power switch, and check that the gas valve is open.
Still no heat after that? Stop there. Gas valves, ignition controls and heat exchangers are jobs for a licensed tech, period. That goes double in North Texas, where most furnaces live in hot, cramped attics and only work a few months a year.
This guide covers both: the fixes you can knock out in about 30 minutes, and the warning signs that mean it’s time to put the screwdriver down.
Key Takeaways
- Most “broken” furnaces aren’t broken. A wrong thermostat setting, a dirty filter, a tripped breaker or a loose door panel causes a big chunk of no-heat calls.
- Texas furnaces fail in their own way. Long idle summers, attic heat, dust and sudden cold fronts all take a toll.
- There are seven fixes a homeowner can safely handle. Anything with gas lines, burners or the heat exchanger isn’t one of them.
- Carbon monoxide is the real danger. If you have a gas furnace, put a working CO detector near every bedroom. No exceptions.
- A fall tune-up heads off most mid-winter breakdowns. Book it before the first cold front, not during it.
Already tried the basics and still freezing? Air Zone Experts offers furnace repair service across Little Elm and nearby DFW cities, with 24/7 emergency service. Give us a call at (214) 430-9059.
Why Furnace Repair in Texas Is Different
Up in Minnesota, a furnace runs hard for six months straight and gets serviced like clockwork. Here? A furnace in Little Elm or Frisco might sit untouched from March to November. Then a blue norther blows in, drops the temperature 30 degrees in one afternoon, and suddenly it has to work all night.
All that downtime causes trouble. Dust settles on the burners and the flame sensor. Bugs and the occasional critter move into vent pipes. And people forget about the filter, because the AC has been doing all the work. In most DFW homes, the furnace and AC share the same blower and the same filter.
Then there’s the attic. A lot of North Texas furnaces live up there, and summer attic temps get way hotter than it is outside. Wiring, rubber hoses, plastic parts and the condensate drain bake for months. By the time you need heat, they’ve taken a beating.
Timing makes it worse. Texas winters are short, but cold snaps hit fast. Remember Winter Storm Uri in February 2021? Heating companies across the state were swamped within hours. When every furnace in Denton County kicks on the same night, repair calls pile up quickly.
So knowing what you can check yourself might save you a long wait.
Safety First: Before You Touch Anything
Troubleshooting a furnace is safe if you follow a few hard rules.
Smell gas? Get out. A rotten-egg smell can mean a gas leak. Don’t flip light switches, don’t touch the thermostat, and don’t go looking for the source. Get everyone outside, then call your gas company or 911 from out there. Atmos Energy and CoServ Gas serve much of North Texas.
CO alarm going off? Get out. Everybody, pets included, goes outside into fresh air, then call 911. Don’t head back in to “check on the furnace.”
Kill the power before opening any panels. Most furnaces have a service switch nearby that looks just like a light switch. In the attic, it’s usually on the unit or right next to it. Flip it off before you take off an access door.
Know where to stop. If a step involves a gas line, a burner or a wiring harness, it’s not a DIY job. It’s not about how handy you are. Mistakes on gas appliances can hurt people.
How to Repair a Furnace: 7 Homeowner-Safe Fixes
Go through these in order. They start with the easiest, most common fixes and work up from there.
1. Check the Thermostat
Sounds too simple. But thermostat settings cause a surprising number of service calls.
- Set the mode to Heat, not Cool or Off.
- Set it at least 3 degrees above the current room temperature.
- Check the fan. If it’s set to On instead of Auto, the blower runs nonstop and pushes room-temperature air between heating cycles. Feels like the furnace is blowing cold.
- Screen dim or blank? Swap the batteries.
- Smart thermostat? See if a schedule or “eco” mode is overriding you.
2. Replace the Air Filter
A clogged filter is the number one cause of furnace trouble. When air can’t flow, heat builds up inside the furnace and a safety part called the high-limit switch shuts the burners off. The blower keeps going, though. So you get cool air and a furnace that seems to quit after a few minutes.
Pull the filter out and hold it up to a light. Can’t see light through it? Replace it. Match the size printed on the frame, and point the airflow arrow toward the furnace. If your AC and furnace share a filter (most Texas homes do), check it every month during heavy-use seasons.
3. Reset the Power
Gas furnaces still need electricity. The ignitor, control board, inducer fan and blower all run on it.
- Look in your electrical panel for a tripped breaker labeled furnace, FAU or HVAC. Flip it all the way off, then back on.
- Make sure the service switch by the furnace is on. It gets bumped more than you’d think, especially in attics people use for storage.
- Check that the blower compartment door is seated all the way. There’s a small safety switch behind it that cuts power if the panel’s loose or crooked.
If the breaker trips again right away, leave it off and call a tech. That’s an electrical problem.
4. Confirm the Gas Supply Is On
Find the shutoff valve on the gas line going into the furnace. Handle running the same direction as the pipe? It’s open. Sitting crosswise? It’s closed.
Quick check: are your other gas appliances, like the water heater or stove, working? If none of them are, the problem’s probably your gas service, not the furnace.
Don’t adjust anything past that valve.
5. Read the Error Code
Most furnaces from the last 20 years or so have a little LED on the control board, which you can see through a small window in the lower panel. It blinks in patterns when something’s wrong.
Count the blinks and match them to the chart on the inside of the furnace door. The code tells you, and your tech, whether it’s a pressure switch, a flame sensing problem, a limit trip or something else. Jot it down before you call. It can make the repair visit shorter.
6. Clear the Condensate Drain
High-efficiency furnaces (usually labeled 90% AFUE or higher) make water as they run. It drains out through a PVC line, often into a pan under attic units. If that line clogs or the pan fills up, a float switch shuts everything down so your ceiling doesn’t get wrecked.
Look for standing water in the pan or a float switch that’s tripped. A wet/dry vac on the outdoor end of the line usually clears the clog. If it’s been overflowing for a while, check the ceiling underneath for stains.
7. Clean the Flame Sensor
The flame sensor is a thin metal rod near the burners. Its job is to confirm the gas actually lit. After a long Texas summer it often gets coated with gunk, and then it can’t “see” the flame. So the furnace lights for a few seconds and shuts right back off.
With the power and gas both off:
- Find the sensor. It’s a single rod held in by one screw, with one wire attached.
- Take out the screw and gently slide the sensor out.
- Rub the rod lightly with fine emery cloth or a fine scrub pad until it’s shiny.
- Put it back exactly the way it came out.
Don’t touch the hot surface ignitor sitting nearby. It’s fragile, and the oils from your skin can shorten its life. If you’re not 100% sure which part is which, skip this one.
Not sure which fix fits your situation? The Air Zone Experts HVAC symptom checker can help narrow it down.
Common Furnace Problems and What They Usually Mean
| Symptom | Likely Causes | Homeowner Step | Call a Pro If |
|---|---|---|---|
| Blowing cold air | Fan set to On, dirty filter, ignition failure | Check thermostat and filter | Burners never light |
| Short cycling (on and off) | Dirty filter, dirty flame sensor, overheating | Replace filter, clean sensor | Still cycling after both |
| Won’t ignite | Failed ignitor, gas supply, pressure switch | Check power and gas valve | Error code points to ignition |
| Burning smell at first startup | Dust burning off the heat exchanger | Let it run, crack a window | Smell lasts hours or smells electrical |
| Loud bang at startup | Delayed ignition from dirty burners | None | Always |
| Squealing or grinding | Worn blower motor or bearings | None | Always |
| Yellow or flickering flame | Incomplete combustion | Turn the furnace off | Always (CO risk) |
| Pilot light out (older units) | Thermocouple, draft | Relight per the label | It won’t stay lit |
A dusty smell the first time you turn on the heat each fall? Totally normal in Texas. A sharp electrical or melting-plastic smell is not. Shut it off at the service switch and call for help.
Repairs That Should Be Done by a Professional
Some furnace repairs look easy on YouTube. In real life, they need tools, training and a license most homeowners don’t have.
Leave these to a tech:
- Gas valve replacement or adjustment. The wrong gas pressure can cause overheating, soot or carbon monoxide.
- Ignitor and control board replacement. Parts have to match exactly, and it’s easy to misdiagnose.
- Inducer motor and pressure switch repairs. These control how combustion gases get vented out of your house.
- Blower motor replacement. It involves capacitors that can hold a dangerous charge even with the power off.
- Heat exchanger inspection. Cracks are often invisible without special tools.
- Vent and flue repairs. Bad venting is a leading cause of CO problems.
There’s a legal side too. In Texas, heating and air conditioning work is licensed through the Texas Department of Licensing and Regulation (TDLR). Hiring a licensed contractor protects you. And DIY or unlicensed repairs on internal parts can void your manufacturer’s warranty.
The Heat Exchanger and Carbon Monoxide
The heat exchanger is what keeps combustion gases away from the air you breathe. Over the years, all that heating and cooling can crack it, and a cracked heat exchanger can leak carbon monoxide into your ductwork.
You can’t see or smell CO. Exposure can cause headaches, dizziness, nausea and fatigue. A big red flag is several people in the house feeling sick at the same time, then feeling better once they leave.
Here’s how to protect your household:
- Put CO detectors on every floor and near the bedrooms.
- Test them every month, and swap the batteries when you change the clocks.
- Replace them by the date printed on the back.
- Get a yearly furnace inspection that includes a heat exchanger check.
Older furnaces, and ones that have overheated again and again from poor airflow, are the most at risk. Yet another reason those filter changes matter.
Winter Prep: Get Ready Before the First Cold Front
The best furnace repair is the one you never need. A few weeks before it gets cold (usually October in North Texas), run through this list:
- Change the air filter.
- Move storage boxes away from the furnace, especially in the attic.
- Make sure furniture or rugs aren’t blocking vents and return grilles.
- Test your CO and smoke detectors.
- Turn the heat on for a test run before you actually need it.
- Book a professional tune-up.
A tune-up usually covers cleaning the burners and flame sensor, testing the safety controls, checking gas pressure, inspecting the heat exchanger and making sure everything’s venting right.
Air Zone Experts offers a yearly maintenance plan for $100 a year. Check out our current maintenance specials for seasonal deals.
When to Call Air Zone Experts
Tried the homeowner checks and still no heat? Or did something in this guide make you nervous about safety? Time to call a pro.
Air Zone Experts is a family-owned HVAC company based in Little Elm. We serve homeowners in Frisco, Prosper, McKinney, Denton, The Colony, Lewisville, Allen and nearby cities. Owner Adrian Racovei runs a lot of the service calls himself.
What you can expect from us:
- Upfront pricing. The price we agree on before we start is the price you pay.
- No pressure. We’ll repair it when a repair makes sense, and tell you straight when it doesn’t.
- All makes and models, including Trane, Carrier, Lennox, Goodman, Rheem and more.
- 24/7 emergency service for those overnight cold snaps.
If your furnace is near the end of the road and replacement is on the table, ask us about financing options. For everything else, take a look at our full range of heating services.
Give us a shout at (214) 430-9059 to schedule a furnace repair or tune-up.