First cold snap of the winter rolls through Central Texas, you switch the thermostat to heat, and... nothing. The furnace will not turn on. Before you call an HVAC tech, there are seven things to check yourself that solve over half of "furnace not turning on" calls. Here is the order to check them in, what each fix costs if you do need a pro, and when to stop troubleshooting and call.
First — Confirm It's Actually Failing to Run
A few quick checks tell you whether the furnace is failing to ignite, failing to start at all, or running but not producing heat:
No air coming from the vents at all: The blower is not running. Either the system is not getting power, the thermostat is not calling for heat, or the blower motor itself has failed.
Air coming from the vents but it's cold: The blower is running but the burner or heating element is not. Pilot light, ignition, gas supply, or heating element issue.
Furnace makes noise but never produces heat: Ignition is trying but failing — flame sensor, igniter, or gas valve issue.
The 7 Things to Check (In Order)
### 1. Is the Thermostat Actually Set Correctly?
More "broken furnaces" are actually thermostats than you would believe. Check:
Mode is set to HEAT (not OFF, not COOL, not AUTO if it is a separate option).
Setpoint is above the current room temperature. Sounds obvious but in spring/fall when the house has been at 70° all day and someone bumps the thermostat to 68° expecting heat, it does nothing.
Batteries are fresh if the thermostat is battery-powered. Many "smart" thermostats display low-battery warnings only on the screen — and a dim or blank screen means no signal to the furnace.
Fan setting is on AUTO (not ON). With fan ON, the blower runs constantly and you cannot tell whether the furnace is firing or just blowing room-temp air.
If you have a smart thermostat (Nest, Ecobee, Honeywell Lyric), open the app and confirm the system is reporting connected and the schedule is not actively in an OFF block.
### 2. Is the Breaker Tripped?
Find your electrical panel and look for a breaker labeled "furnace," "HVAC," or "air handler." Most furnaces are on a 15-amp single-pole breaker. If it is in OFF or halfway between ON and OFF, it has tripped.
Flip it fully to OFF, then to ON. If it stays on, you may have just had a transient trip and you are good. If it trips again, do not keep resetting — repeated tripping means a short or a failing component, and resetting can damage things further.
### 3. Is the Furnace Power Switch On?
Most furnaces have a regular wall light switch mounted near the unit (in the attic, closet, or basement) that controls power to the furnace. It looks like a normal light switch and is often unlabeled. If someone was up in the attic and bumped it, or if a switch got flipped during a recent remodel, the furnace has no power.
Find the switch — it is usually within 6 feet of the furnace. Flip it on. If you hear the furnace come to life, you found the problem.
### 4. Is the Air Filter Severely Clogged?
Most modern furnaces have a safety switch that prevents them from running with severely restricted airflow. A clogged filter can trip this switch and lock out the furnace.
Pull the filter. If it is heavily caked with dust and debris, replace it. If you cannot remember the last time you changed it, change it now. Then turn the system OFF at the thermostat for 5 minutes, turn it back on, and call for heat.
### 5. Is the Pilot Light Out? (Older Gas Furnaces)
Furnaces installed before about 2010 often have a standing pilot light. If it is out, the furnace will not fire.
Look for a small access panel on the furnace front. Behind it, you can usually see the pilot. The relighting procedure varies by model but is typically printed on a sticker inside the panel. The general steps: turn the gas valve to PILOT, hold down the pilot button while pressing the igniter, hold the button for 30 seconds after the pilot lights, then turn the gas valve to ON.
If the pilot will not stay lit, the thermocouple has failed — a $150–$250 repair on a gas furnace.
Modern furnaces (post-2010) use electronic ignition and do not have a standing pilot. Skip this step if your furnace was installed in the last 15 years.
### 6. Is the Condensate Drain Clogged? (High-Efficiency Furnaces Only)
High-efficiency furnaces (90%+ AFUE) produce condensation as a byproduct of combustion. The condensate drains through a small PVC line. If that line clogs — common in Texas because of mineral buildup — the furnace will lock out as a safety measure.
Look for a clear or white plastic line draining from the bottom of the furnace, usually to a floor drain or condensate pump. If there is water pooled in the pump or the line looks blocked, that is your issue. Some homeowners can clear it with a wet/dry vacuum on the discharge end. Otherwise it is a $150–$250 service call.
### 7. Is the Furnace Door Closed Properly?
Most furnaces have a door safety switch that prevents the unit from running if the front access panel is not fully seated. If you (or a previous tech) had the panel off and did not snap it back on completely, the furnace will not start.
Push the panel firmly into place. Listen for a click as the safety switch engages. Try the thermostat again.
What Each Fix Actually Costs
DIY checks (thermostat batteries, breaker, switch, filter, pilot relight): $0
Thermocouple replacement: $150–$250
Flame sensor cleaning or replacement: $150–$300
Hot surface igniter replacement: $200–$350
Condensate line clearing: $150–$250
Capacitor replacement: $150–$300
Blower motor replacement: $400–$800
Inducer motor replacement: $400–$700
Gas valve replacement: $400–$700
Control board replacement: $400–$800
Heat exchanger replacement (rare, but expensive): $1,500–$3,500 — at this cost, replacement is often better than repair on older units
When to Stop and Call Right Away
If you smell gas: Stop everything. Leave the house, leave the door open, call your gas utility from outside. Do not run the furnace, do not light anything. Get the leak fixed first.
If you hear a loud bang when the furnace tries to fire: Could be delayed ignition — a buildup of gas igniting all at once. Turn the system OFF and call. Repeated delayed ignition can crack the heat exchanger.
If the breaker trips repeatedly: Stop resetting. Call a pro.
If the furnace runs but produces no heat (cold air from vents): Likely an ignition or gas supply issue. Turn off and call.
Same-Day Heating Service
We service heating systems across Central Texas year-round — Pflugerville, Bastrop, Taylor, Elgin, Georgetown, Hutto, Manor, Cameron, Rockdale, Brenham, and our full service area. Same-day diagnosis on furnace issues. Call (737) 260-7255. Texas license TACLB00027491E. Flat-rate pricing — the quote is the price.