Why Did My Furnace Stop Producing Heat?
If your furnace isn't producing heat, work these checks in order before calling anyone: confirm the thermostat is set to Heat and a few degrees above room temp, replace the air filter if it's been in 30+ days, verify the furnace switch (the light-switch-style switch on or near the unit) is on, check the gas-valve handle, look for a tripped breaker, and listen for the inducer fan and ignitor cycling. The fix ranges from $0 (filter or switch) to $4,000 (heat-exchanger replacement, which always means full furnace replacement — we never repair cracked heat exchangers).
In my 8+ years running Frosty's HVAC, I've walked into hundreds of homes across Farmers Branch, Irving, Coppell, Flower Mound, Lewisville, and Grapevine where the furnace stopped producing heat. EPA 608 #2396328, license TACLA126718E (Mariafernanda Jacobo). Texas winters are unpredictable — a 70°F day in January, a 30°F night following — and when that cold snap hits, your furnace has often been sitting idle for months. Knowing what you can safely check yourself, and when to call a professional, is the difference between a $0 fix and a 4-hour emergency call.
Texas winters are unpredictable. We might have a 70°F day in January followed by a 30°F night. When that cold snap hits, your furnace needs to fire up and work — and it's usually been sitting idle for months. That idle period is when problems develop. Here's what to check, step by step.
Is Your Thermostat the Reason the Furnace Won't Start?
I know this sounds basic, but I'd estimate 10-15% of "my furnace isn't working" calls turn out to be thermostat issues. Here's what to verify:
- Mode: Make sure it's set to "Heat" — not "Cool" or "Off." It happens more than you'd think, especially if someone bumped it.
- Temperature setting: Set it at least 3-5 degrees above the current room temperature. If it's set to 70°F and the room is already 69°F, the furnace won't kick on.
- Fan setting: Set it to "Auto." If it's on "On," the blower runs continuously and blows unheated air between cycles, making it feel like the furnace isn't working.
- Batteries: If your thermostat is battery-powered, replace them. Dead batteries cause a blank or frozen screen and the system won't get the signal to turn on.
If you have a Frosty Thermostat (our smart thermostat included with all system installations), you can check all of this from your phone.
Can a Dirty Air Filter Really Shut Down a Furnace?
A clogged air filter is the single most common cause of furnace problems. When the filter is packed with dust, pet hair, and debris, it restricts airflow. The furnace overheats, the high-limit safety switch trips, and the system shuts down. In many cases, it'll try to restart, overheat again, and lock out completely.
Your filter is typically located in the return air grille on a wall or ceiling, or in a slot at the furnace itself (usually in a closet or attic in Texas homes — we don't have basements here). Pull it out and hold it up to a light. If you can't see light through it, replace it. Use a standard 1-inch pleated filter, MERV 8-11. Don't go higher than MERV 13 unless your system is designed for it — too-restrictive filters cause the same airflow problems as dirty ones.
What If the Furnace Circuit Breaker Keeps Tripping?
Your furnace has its own breaker in your electrical panel, and so does your thermostat circuit in some homes. Check both. If a breaker has tripped, flip it fully off and then back on. If it trips again immediately, stop — that's an electrical fault and you need a professional. Don't keep resetting a tripping breaker.
How Do You Know If It's a Gas Supply Problem?
If you have other gas appliances (water heater, gas stove), check if they're working. If nothing gas-powered is working, the issue might be at the gas meter or supply line — call your gas utility (Atmos Energy in DFW: 1-866-322-8667). If other appliances work but the furnace doesn't, check the gas shutoff valve on the gas line near the furnace. The handle should be parallel to the pipe (open). If it's perpendicular (turned 90 degrees), it's shut off.
Safety warning: If you smell gas (rotten egg odor) at any point, leave the house immediately, don't flip any switches or light anything, and call 911 or Atmos Energy from outside. Gas leaks are not DIY territory. The CDC's carbon monoxide safety guidance also explains why any malfunctioning gas-burning furnace deserves immediate attention.
How Do I Know If the Furnace Ignitor Has Failed?
Modern furnaces (anything made in the last 25 years) don't have a standing pilot light. They use a hot surface ignitor — a small ceramic element that glows red-hot to ignite the gas. These ignitors are fragile and wear out every 5-8 years. When they fail, the furnace tries to start, can't light the gas, and shuts down after a few attempts.
You can sometimes see the ignitor through the small window on your furnace cabinet. When the furnace tries to start, you should see a bright orange glow. If the blower starts but you never see the glow, the ignitor has likely failed.
Can you replace it yourself? Technically, yes — it's usually two screws and a plug. But if you're not comfortable working around gas lines and electrical connections, call a pro. An ignitor replacement costs $350-$500 from us, which includes the $85 diagnostic (waived when you approve the repair).
Why Does the Furnace Light for a Few Seconds Then Shut Off?
The flame sensor is a small metal rod that sits in the burner flame. Its job is to confirm gas is actually burning. If it doesn't detect flame within a few seconds of the gas valve opening, the furnace shuts down the gas as a safety measure. Over time, the sensor gets coated with carbon buildup and can't detect the flame even when it's burning perfectly.
A dirty flame sensor is one of the most common furnace repairs I do. The symptom is distinctive: the furnace lights, runs for 5-10 seconds, then shuts off. It'll retry 2-3 times, then lock out. Flame sensor cleaning or replacement costs $350 at Frosty's HVAC. Again, the $85 diagnostic fee is waived with the repair.
When Should You Stop Troubleshooting and Call a Licensed Tech?
Everything above Step 4 is getting into territory where most homeowners should call for help. But there are specific situations where you absolutely need a licensed HVAC technician — you can verify any DFW tech's license through the TDLR license search before they step inside:
- You smell gas: Evacuate and call 911. Period.
- The furnace is making loud banging sounds at startup: This could be delayed ignition — gas is pooling before igniting, causing a small explosion inside the combustion chamber. This is dangerous and can crack the heat exchanger.
- You see a cracked heat exchanger: If your furnace has visible cracks, rust holes, or soot stains on the heat exchanger, shut it off. A cracked heat exchanger can leak carbon monoxide into your home. Replacement costs $2,500-$4,000. In many cases, if the furnace is older than 15 years, full replacement makes more sense.
- The gas valve isn't working: If the ignitor glows but gas never flows, the gas valve may have failed. This is a $800-$1,200 repair and requires a licensed technician.
- Multiple lockouts: If you've reset the furnace 3+ times and it keeps locking out, something is genuinely wrong. Continuing to reset it can cause secondary damage.
How Much Do Common Furnace Repairs Cost in DFW?
Here's what our customers in the DFW area actually pay for the most common gas furnace repairs:
- Diagnostic fee: $85 (waived if you approve the repair)
- Ignitor replacement: $350-$500
- Flame sensor cleaning/replacement: $350
- Gas valve replacement: $800-$1,200
- Blower motor: $750-$1,500 (ECM/variable speed motors up to $2,800)
- Heat exchanger replacement: $2,500-$4,000
These are flat-rate prices — we quote the job, not by the hour. You'll know exactly what it costs before we start work.
How Can You Prevent Furnace Failures Next Winter?
The best way to avoid a cold house on a 30°F Texas night is to have your furnace inspected before you need it. Our Frosty Club Premium membership ($300/year) includes 2 tune-ups per year — one for your AC in spring and one for your furnace in fall. We catch ignitor wear, flame sensor buildup, cracked heat exchangers, and gas valve issues before they leave you without heat.
Read our full HVAC maintenance checklist for everything you can do yourself between professional visits.
Need a Licensed DFW Furnace Technician Today?
If your furnace isn't heating and you've checked the basics above, call us at (469) 254-0548. We serve Farmers Branch, Coppell, Irving, Flower Mound, Lewisville, and Grapevine. Our $85 diagnostic fee is waived when you approve the repair — so you only pay for the fix, not the visit.
— Omar Jacobo, Owner, Frosty's HVAC | EPA 608 #2396328 | TACLA126718E
Call Now