The thermostat’s set right, gas is on, but nothing happens. Before you call around, check the ignitor. Nine times out of ten that small ceramic piece is the whole problem.
What a Furnace Ignitor Does
The ignitor is the spark that starts your whole heating sequence. In most modern forced air furnaces it’s a hot surface ignitor (HSI), a fragile silicon nitride or silicon carbide element that heats to around 2,500°F to ignite the gas burners.
Without a clean ignitor, the burners never light. The furnace cycles repeatedly, you hear clicking, nothing happens.
Two Ignitor Types You’ll Encounter
Hot Surface Ignitor (HSI)
Most common in modern gas furnaces. It looks like a thin, flat probe near the burner assembly.
Direct Spark Ignitor
Uses an electrical arc. Commonly found in older units and some boilers.
Key Takeaway: Touching the ignitor element with bare skin deposits oils that cause premature failure. Always hold it by the base or ceramic bracket, never the element itself.
How to Clean a Furnace Ignitor Step by Step
Before you start, turn the power off at the breaker, shut off the gas supply, and wait at least 30 minutes for everything to cool.
Step 1: Remove the Furnace Access Panel
Use a screwdriver to remove the furnace access panel.
Step 2: Locate the Ignitor
Find the ignitor near the burner assembly using a flashlight if necessary.
Step 3: Disconnect the Wiring
Carefully disconnect the push on wire connector.
Step 4: Remove the Ignitor
Unscrew the mounting bracket while holding only the base.
Step 5: Inspect for Damage
Look for cracks, heavy carbon deposits, or discoloration.
Step 6: Clean the Ignitor
Use short bursts of compressed air to clear loose debris.
If buildup remains, gently wipe it with a fine scuff pad or a lint free cloth dampened with isopropyl alcohol.
Step 7: Allow It to Dry
Let the ignitor dry completely before reinstalling.
Step 8: Reinstall and Test
Reconnect the wires, reinstall the access panel, restore power, and test the furnace.
Tools You’ll Need
- Screwdriver set
- Compressed air
- Fine scuff pad or lint free cloth
- Isopropyl alcohol
- Flashlight
Key Takeaway: If you see visible cracks or the ignitor glows orange instead of bright orange white, cleaning won’t fix it. Replacement runs $20 to $80 for the part.
When DIY Doesn’t Make Sense
Some situations belong to a licensed heating contractor, not a YouTube tutorial:
- Ignitor shows physical damage or an irregular glow pattern
- Furnace short-cycles after cleaning
- You smell gas at any point during the process
- The flame sensor and ignitor are both coated (this usually signals a combustion or draft issue, not just dust)
Key Takeaway: If you’ve cleaned the ignitor and the furnace still won’t stay lit, stop troubleshooting and get a technician in.
Why Missoulians Call Right Now Plumbing and Heating
Companies like Garden City, Hellgate, and Temp Right have been around Missoula for a while. But response time, quality of work, and same day availability are where Right Now stands apart.
We dispatche same day, runs arrival windows with live text updates, and keeps trucks stocked for first visit fixes all over town including Miller Creek, Linda Vista, the South Hills, Lolo, and more!
Call Right Now Plumbing and Heating
Phone: (406) 625-7690
Frequently Asked Questions
How do I know if my furnace ignitor is dirty?
Your furnace will attempt to start, you may hear clicking or the blower kick on, but the burners never light.
Can I clean a furnace ignitor without replacing it?
Yes, if there’s no physical damage. Use compressed air and a fine scuff pad or isopropyl-dampened cloth while handling only the base.
How often should a furnace ignitor be cleaned?
Once a season at minimum, ideally before the heating season starts. In dusty homes or older furnaces, twice a year is reasonable.
What happens if I touch the ignitor element with my fingers?
Skin oils transfer to the element and create hot spots during operation, accelerating cracking and failure. Always handle the ignitor by the ceramic base.
How long does a furnace ignitor last?
Typically 4 to 7 years. Frequent short-cycling, dirty filters, and poor combustion conditions can shorten that lifespan significantly.
What’s the difference between an ignitor and a flame sensor?
The ignitor lights the gas. The flame sensor verifies the burner is lit and keeps the gas valve open. Both can fail due to buildup and are often serviced together.
Should I replace or clean my furnace ignitor?
Clean it if it’s intact and only coated with carbon or dust. Replace it if you see cracks, a dull or irregular glow, or if the furnace still fails after cleaning.
Is cleaning a furnace ignitor safe for a homeowner?
It can be, provided you follow proper lockout procedures. If you’re uncertain at any point, call a licensed HVAC technician.
Written by the owner of Right Now Plumbing and Heating in Missoula, MT.
Sources
- U.S. Energy Information Administration — approximately half of U.S. households heat with natural gas (2024)
- Family Handyman — furnace ignitor cleaning guidance (updated October 2024)
- Sears Home Services — furnace ignitor maintenance procedures (2025)
- Right Now Plumbing and Heating Google Reviews via Trustindex verification