Quick Answer
If your furnace won't ignite, check your thermostat settings, gas valve, power switch, and air filter first—these solve about 30% of cases. The most common causes requiring repair are a failed ignitor ($105-$275), dirty flame sensor ($75-$150 cleaning), or gas valve issues ($200-$600).
When your furnace won't ignite, you're left without heat—and in Charlotte's winters, that's not just uncomfortable, it can be dangerous. The good news: many ignition problems have simple causes you can check yourself. The bad news: some require professional repair. Here's how to tell the difference and get your heat back fast.
Quick Troubleshooting: Check These First
Before calling for furnace repair, run through these quick checks—they solve the problem about 30% of the time and cost you nothing:
5-Minute Ignition Troubleshooting
- 1
Check Your Thermostat
Make sure it's set to "Heat" mode, the temperature is set above the current room temperature, and the batteries aren't dead. This sounds obvious, but it's the #1 "fix" we see.
- 2
Check the Gas Valve
Find the gas valve near your furnace (usually a yellow handle). It should be parallel to the gas line (open). If it's perpendicular, turn it to open.
- 3
Check the Power Switch
Furnaces have a power switch that looks like a light switch, usually on the side or nearby. Make sure it's ON. Also check your circuit breaker.
- 4
Check the Air Filter
A severely clogged filter can cause the furnace to overheat and shut down. Pull it out and check—if it's black or you can't see through it, replace it.
- 5
Reset the Furnace
Turn off the power switch, wait 30 seconds, then turn it back on. This clears error codes and lets the ignition sequence restart.
Safety First
Common Causes: Why Your Furnace Won't Ignite
If the quick checks didn't solve it, here are the most common causes of furnace ignition failure—ranked by how often we see them:
1. Faulty Ignitor (Most Common)
Modern furnaces use either a hot surface ignitor (HSI) or intermittent pilot ignitor. These components glow red-hot to ignite the gas. They wear out over time—most last 3-7 years—and are the #1 cause of ignition failure. Symptoms include: furnace clicks and hums but no flame appears, or you see a dim glow instead of bright orange.
Ignitor Replacement Costs
| Component | Parts | Labor | Total |
|---|---|---|---|
| Hot Surface Ignitor | $30-$80 | $75-$150 | $105-$230 |
| Intermittent Pilot | $40-$100 | $100-$175 | $140-$275 |
| Ignitor + Flame Sensor | $60-$120 | $125-$200 | $185-$320 |
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2. Dirty Flame Sensor
The flame sensor is a small rod that detects whether the burners lit. When it gets dirty (carbon buildup), it can't sense the flame and shuts off the gas as a safety measure. This causes the furnace to ignite briefly then shut off, or fail to stay lit. Cleaning the flame sensor is a quick, inexpensive fix—usually $75-$150 for a service call.
Nick, Kodiak Owner
3. Gas Supply Issues
No gas = no ignition. Check that your gas valve is open, you have gas service (check other gas appliances), and your gas bill is paid. If only the furnace has issues, the gas valve on the furnace itself may be stuck or faulty. Gas valve replacement runs $200-$600.
4. Pressure Switch Problems
The pressure switch confirms the inducer motor is creating proper airflow before allowing ignition. A stuck or faulty pressure switch, blocked exhaust vent, or failed inducer motor can all prevent ignition. Listen for the inducer motor (a humming/whooshing sound that starts before ignition attempts). If you don't hear it, that's likely your problem.
5. Control Board Failure
The control board orchestrates the entire ignition sequence. When it fails, the furnace may not attempt ignition at all, or may error out mid-sequence. Control board replacement is a major repair ($400-$800) but is less common than the issues above.
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The Ignition Sequence: What Should Happen
Understanding the normal ignition sequence helps you identify where things are going wrong:
Normal Furnace Ignition Sequence
- 1
Thermostat Calls for Heat
The thermostat signals the furnace that heat is needed.
- 2
Inducer Motor Starts
You'll hear a humming/whooshing sound as the inducer motor creates airflow through the heat exchanger.
- 3
Pressure Switch Closes
The pressure switch confirms proper airflow. No click here means a pressure switch or airflow problem.
- 4
Ignitor Heats Up
The ignitor glows orange-hot (15-60 seconds depending on type). If it doesn't glow, the ignitor is likely failed.
- 5
Gas Valve Opens
The gas valve opens, releasing gas to the burners.
- 6
Ignition Occurs
Gas ignites. You should see blue flames with small yellow tips.
- 7
Flame Sensor Confirms
The flame sensor detects the flame and keeps the gas valve open. If it doesn't sense flame, gas shuts off in 3-5 seconds.
- 8
Blower Motor Starts
After 30-90 seconds of heating, the blower pushes warm air through your ducts.
When to Call a Professional
While some troubleshooting is safe for homeowners, furnace repair involves gas and electricity—both potentially dangerous. Call a professional if:
- You smell gas anywhere in your home
- The quick troubleshooting steps didn't work
- You're not comfortable working around gas appliances
- The furnace is making unusual sounds (banging, screeching)
- You see error codes flashing on the furnace
- The problem keeps recurring after DIY fixes
- Your furnace is over 15 years old (may be time for replacement)
What to Expect from a Service Call
Preventing Future Ignition Problems
Most ignition failures are preventable with regular maintenance:
Ignition Prevention Checklist
- Change your air filter every 1-3 months
- Schedule annual furnace maintenance (ideally in fall)
- Keep the area around your furnace clear of debris
- Listen for changes in startup sounds
- Replace ignitors proactively at 5-7 years old
- Don't skip maintenance because "it's working fine"
Kodiak HVAC Team
Bottom Line
When your furnace won't ignite, start with the simple checks: thermostat, gas valve, power, and filter. These solve about 30% of cases. For the remaining 70%, you're likely dealing with a failed ignitor, dirty flame sensor, or other component that needs professional attention. The good news: most ignition repairs are relatively affordable ($100-$400) and can be completed same-day.
If you're in the Charlotte area and your furnace won't ignite, Kodiak offers same-day furnace repair service. We've been fixing furnaces in Union County and South Charlotte since 2008, and we don't work on commission—so you'll get an honest diagnosis, not a sales pitch.
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Written by
Kodiak HVAC Team
HVAC professional at Kodiak Heating & Cooling.