Furnace Blowing Cold Air?
Your furnace blower is running but the air isn't warm. Here's why and what you can do.
💡 Quick Stat: Check your thermostat fan setting first—if set to ON instead of AUTO, blower runs even when not heating.
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Check These First (DIY)
Before calling for service, try these quick troubleshooting steps.
Check thermostat fan setting
If set to ON, blower runs continuously. Set to AUTO so it only runs when heating.
Wait for warm-up cycle
Furnaces blow cool air for 30-60 seconds at startup before heating begins.
Check and replace air filter
Clogged filter causes overheating—safety shuts off burner but blower keeps running.
Check pilot light (older furnaces)
If pilot is out, furnace can't heat. Follow relighting instructions on unit.
Check gas supply
Ensure gas valve near furnace is ON (handle parallel to pipe, not perpendicular).
Tried everything above and still having issues?
Our technicians can diagnose the problem in about 30 minutes.
Schedule Service: (704) 821-3632Common Causes & Repair Costs
What might be wrong and what it typically costs to fix.
| Cause | Likelihood | Cost | DIY? |
|---|---|---|---|
Fan Set to ON Instead of AUTO Fan runs continuously regardless of heating cycle. Simple setting fix. | Very Common | Free | ✓ Yes |
Dirty Air Filter Causes overheating—burner shuts off but blower keeps running. | Very Common | $5-$30 | ✓ Yes |
Pilot Light Out (older furnaces) No pilot = no ignition. Can often relight yourself. | Common (older units) | Free-$150 | ✓ Yes |
Dirty Flame Sensor Sensor doesn't detect flame, shuts off gas. Burner lights briefly then stops. | Common | $100-$250 | Pro |
Ignitor Failure Ignitor won't glow, so burner never lights. | Common | $200-$400 | Pro |
Overheating/Limit Switch Trip Safety switch trips due to overheating. Often caused by dirty filter or blocked vents. | Moderate | $150-$300 | Pro |
Gas Valve Failure Valve stuck closed, no gas reaches burner. | Less Common | $300-$600 | Pro |
Fan Set to ON Instead of AUTO
DIYFan runs continuously regardless of heating cycle. Simple setting fix.
Dirty Air Filter
DIYCauses overheating—burner shuts off but blower keeps running.
Pilot Light Out (older furnaces)
DIYNo pilot = no ignition. Can often relight yourself.
Dirty Flame Sensor
ProSensor doesn't detect flame, shuts off gas. Burner lights briefly then stops.
Ignitor Failure
ProIgnitor won't glow, so burner never lights.
Overheating/Limit Switch Trip
ProSafety switch trips due to overheating. Often caused by dirty filter or blocked vents.
Gas Valve Failure
ProValve stuck closed, no gas reaches burner.
Diagnose by Symptom
Describe what you're experiencing to narrow down the cause.
"Air is cold all the time, never heats"
Likely cause: Ignitor failure, gas supply issue, or thermostat set wrong.
"Heat comes on briefly then blows cold"
Likely cause: Dirty flame sensor (most common) or overheating issue.
"Cold air only when I first turn on the furnace"
Likely cause: Normal—furnaces take 30-60 seconds to start producing heat.
"Blower never stops, even between heating cycles"
Likely cause: Thermostat fan setting is ON instead of AUTO.
Our Repair Pricing
Upfront, honest pricing. No surprises.
$89
Diagnostic Fee
Waived with repair
$200-$800
Most Repairs
20-45 minutes
Response Time
30-50%
Less Than Big Co's
* Prices shown are typical ranges. Final price depends on specific diagnosis.
Serving the Charlotte Metro Area
Same-day emergency service available • Response in 20-45 minutes
Frequently Asked Questions
Why is my furnace blowing cold air?
First, check your thermostat fan setting—if it's set to ON instead of AUTO, the blower runs continuously even when not heating. Next common causes: dirty air filter causing overheating (burner shuts off), failed ignitor, or dirty flame sensor. Check filter first—it's the easiest fix.
Why does my furnace blow cold air then turn off?
This usually indicates the burner lights but then shuts off. Most common cause: dirty flame sensor that doesn't detect the flame, so the furnace shuts off gas as a safety measure. Cost to fix: $100-$250. Could also be overheating from dirty filter.
Is it normal for furnace to blow cold air at first?
Yes—for 30-60 seconds. Furnaces have a "pre-purge" cycle where the blower runs to clear the heat exchanger before ignition. If cold air continues beyond a minute or two, there's a problem.
How much does it cost to fix a furnace blowing cold air?
Depends on cause. Filter replacement: $5-$30 (DIY). Flame sensor cleaning/replacement: $100-$250. Ignitor: $200-$400. Most repairs: $200-$800. Our $89 diagnostic is waived with repair.
Related Troubleshooting Guides
Still Getting Cold Air?
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