Last updated: 2026-05-01
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Furnace Not Igniting
Thermostat calls for heat but furnace doesn't fire up
85%
85% chance this is caused by:
Dirty flame sensor or failed hot surface igniter
🔧 The Exact Part You Need
Total parts cost: $40. Same-day shipping available on most items.
🔨 Tools You'll Need
Easy · 15-20 minutes
Parts: $40 vs $$2,500-6,000 to replace
📋 Step-by-Step Instructions
1
Turn off power and gas to the furnace
2
Remove the front panel
3
Locate the flame sensor (thin metal rod near the burners)
4
Remove it (usually one screw)
5
Clean it gently with emery cloth or steel wool
6
Reinstall and test — if it still won't ignite, replace the igniter
7
Igniter is fragile — don't touch the gray element with bare hands
Other Furnace Problems
Frequently Asked Questions
How much does it cost to fix a furnace that's not igniting?
The part costs about $25. If you do it yourself, that's your total cost. A professional service call would add $100-200 in labor, bringing the total to $175.
How long does this furnace repair take?
This repair is rated "easy" and typically takes 15-20 minutes. The most time-consuming part is usually accessing the component, not the actual swap.
What if this isn't the problem?
Our diagnosis is 85% likely based on the symptom you described. If replacing this part doesn't fix it, the next most common cause for "thermostat calls for heat but furnace doesn't fire up" would be related to the wiring harness or control board. In that case, consider calling a professional.
Should I just replace my furnace instead?
A new furnace costs $2,500-6,000. If yours is well under 15-20 years old, a $25 repair is far more cost-effective. If it's near end-of-life and has had multiple issues, replacement starts making more sense.