Furnace Not Igniting
Thermostat calls for heat but furnace doesn't fire up
85% chance this is caused by:
Dirty flame sensor or failed hot surface igniter
Furnace not igniting is a professional-only-difficulty repair. The most likely cause is dirty flame sensor or failed hot surface igniter, and replacing the failed part takes approximately 15-20 minutes. The part costs about $40 — compared to $2,500-6,000 for a full replacement.
Fix it this weekend. Most parts ship same-day on Amazon.
A service call costs $150-300. This repair takes about 15-20 minutes and the part runs $40. Order the part tonight, fix it Saturday morning.
✓ This repair requires professional expertise. Your instinct to research before attempting it was the right call — some repairs are best left to licensed technicians.
Safety Warning
Turn off gas supply at the shutoff valve before servicing. If you smell gas at any point, evacuate and call your gas company. Furnaces use high voltage and contain combustible gas. Hire a professional for any work involving the heat exchanger, gas valve, or ignition system.
🔧 The Exact Part You Need
Total parts cost: $40. Same-day shipping available on most items.
Find the Right Part for Your Furnace
Parts vary by model. Search with your model number for the best match.
Tip: Add your model number (e.g. "GE GSS25GSH") for more precise results.
🔥 Parts for Furnaces move fast on Amazon — especially common failure parts like these.
🔨 Tools You'll Need
Repair Summary
| Appliance | Furnace |
| Problem | Not Igniting |
| Diagnosis Confidence | 85% |
| Most Likely Cause | Dirty flame sensor or failed hot surface igniter |
| Difficulty | professional-only |
| Estimated Time | 15-20 minutes |
| Parts Cost | $40 |
| Replacement Cost | $2,500-6,000 |
⚠️ Professional Repair Required
This repair involves lethal hazards and should only be performed by a trained professional.
The information below explains what is likely wrong with your furnace so you can make an informed decision when speaking with a repair technician.
Turn off power at the breaker. Do NOT turn off the gas — leave that to a professional.
The most common cause of a furnace not igniting is a dirty flame sensor. This is a thin metal rod near the gas burners.
Other possible causes: failed igniter, bad gas valve, tripped limit switch, or dirty air filter restricting airflow.
Because this repair involves working near gas burners and combustion components, it is strongly recommended to hire an HVAC technician. A professional can diagnose and fix this in one visit, typically for $150-300.
Order the part your technician will need
Knowing the likely failed part before you call saves time and money. Order it now so it is ready when your technician arrives.
Don't put this off.
A Furnace that's failing can cause water damage, electrical issues, or food spoilage — each costing 10x what the replacement part costs. The fix is straightforward. The part is cheap. The risk of waiting isn't.
🔍 Why This Happens
Root cause analysis for your furnace's not igniting
The hot surface igniter in your furnace degrades through repeated high-temperature cycles that stress the material. Each heating cycle causes thermal expansion and contraction — over time, the element fatigues and develops micro-fractures or the thermal safety device trips permanently. This is one of the most common failure modes for this appliance type, especially in units over 5 years old.
85%
Diagnostic match rate
Call a pro
DIY success rate
15-20 minutes
Typical repair time
🛡️ Prevention Tips
How to prevent your furnace's not igniting from happening again after this repair.
Replace the air filter every 1-3 months during heating season. A dirty filter is the #1 cause of premature furnace component failure.
Have the system inspected annually before heating season. A technician can catch wear on the igniter, flame sensor, and heat exchanger early.
Keep all vents and registers open and unblocked. Closed vents create pressure imbalances that stress the blower motor.
Don't store items near the furnace — restricted airflow and combustible materials near the unit are safety and performance hazards.
If you're replacing a thermal component, consider replacing related safety devices at the same time. The hot surface igniter likely stressed surrounding parts.
Other Furnace Problems
Common Questions About This Repair
How much does it cost to fix a furnace that's not igniting?
How long does this furnace repair take?
What if this isn't the problem?
Should I just replace my furnace instead?
🔧 Repair Data Sources
Repair guides are compiled from:
- • Manufacturer service manuals and technical bulletins
- • Common failure pattern data from appliance repair technicians
- • OEM parts databases for exact replacement compatibility
Difficulty ratings are based on the average homeowner's skill level, not professional standards. Confidence percentages reflect the likelihood that the listed cause matches the observed symptom. Updated May 2026.
Disclaimer: This repair guide is for informational purposes only and is based on manufacturer service manuals and published repair data. TheFixGuide is not responsible for any damage, injury, or loss resulting from attempted repairs. If a repair involves gas, high voltage, stored energy (capacitors), or refrigerant, we strongly recommend hiring a licensed professional.
🔨 Need tools? Get parts on Amazon
Get Parts →Dex A. Varland
Master Appliance Technician · 15+ Years Experience
Dex A. Varland is a master appliance technician with 15+ years of hands-on experience across all major brands. He has diagnosed and repaired thousands of household appliances and contributes to TheFixGuide to help homeowners tackle repairs with confidence.
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