A failed furnace ignitor is one of the most common causes of a furnace lockout. Replacing it is a straightforward DIY task that can save you upwards of $300 in HVAC service fees.
In this guide, I’ll walk you through how to identify a burnt-out ignitor, the essential safety steps to take before you begin, and a step-by-step replacement process to get your home warm again.
Quick Guide: How to Replace Your Furnace Ignitor
- 1. Cut the Power and Gas: Flip the furnace service switch to OFF and turn the manual gas valve handle so it is perpendicular to the pipe.
- 2. Open the Cabinet: Remove the furnace access panels to locate the burner assembly and the ignitor (look for the wires leading to a small ceramic base).
- 3. Unplug the Harness: Gently squeeze and pull the plastic wire connector to disconnect the old ignitor from the furnace.
- 4. Remove the Mounting Screw: Using a nut driver or screwdriver, remove the single screw holding the ignitor bracket in place and carefully slide the old unit out.
- 5. Install the New Ignitor: Slide the new part into place. Do not touch the gray element with your bare fingers. Secure it with the mounting screw.
- 6. Reconnect and Test: Plug the wire harness back in, replace the furnace panels, and restore the power and gas. Set your thermostat to "Heat" to confirm the burners ignite.
Table of Contents
- Is Your Ignitor Actually Broken?
- Preparation: Tools and Safety First
- Step-by-Step Replacement Guide
- Troubleshooting Common Failures
Is Your Ignitor Actually Broken?
Because a furnace can fail for several reasons—like a tripped limit switch or a dirty flame sensor—performing a quick "triage" will save you time and money.
Here is how to tell if your ignitor has reached the end of its life.
The Visual Inspection
The most common type of ignitor is a Hot Surface Ignitor (HSI), which is made of a ceramic base and a gray silicon carbide or silicon nitride element.
- Look for Cracks: Open your furnace’s burner cabinet and find the ignitor. If you see a tiny "hairline" crack on the dark gray element, it’s broken.
- Identify Burn Marks: A failed ignitor often leaves behind a small white or yellowish "hot spot" or a scorched mark where the electrical path was severed.
The "Glow" Test
Modern furnaces follow a specific sequence of operation. You can watch this process to see where it fails:
- The thermostat calls for heat.
- The draft inducer motor (a small fan) turns on to clear the exhaust.
The Test: After about 30–60 seconds, look through the furnace's small sight glass or open the panel. You should see a bright orange glow.
The Verdict: If the inducer motor runs for a minute and you never see an orange glow before the furnace shuts itself down, the ignitor is almost certainly dead.
The Multimeter Test
If you want 100% certainty, you can test the part using a digital multimeter.
- Set your meter to Ohms (Ω).
- Disconnect the ignitor from the furnace’s wiring harness.
- Place one probe on each of the two pins inside the ignitor’s plug.
An ignitor typically reads between 40Ω and 90Ω. If your meter reads "OL" (Open Line) or infinite resistance, the internal circuit is broken, and it’s time for a replacement.
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Preparation: Tools and Safety First
Before you reach for your toolkit, remember that you are working with high-voltage electricity and flammable gas. Taking five minutes to prep correctly ensures the job is done safely and prevents you from accidentally damaging your new part.
The "Safety First" Checklist
Do not skip these steps. Even if the furnace isn't currently running, it can still deliver a dangerous shock or leak gas if handled improperly.
- Kill the Power: Locate the service switch (it looks like a standard light switch) on the side of the furnace or nearby wall and flip it to OFF. For extra security, turn off the dedicated furnace breaker in your home's electrical panel.
- Shut Off the Gas: Turn the manual gas valve (usually a yellow or red handle on the incoming pipe) to the OFF position (perpendicular to the pipe).
- Let it Cool: If your furnace was recently attempting to cycle, the burner box components might still be hot. Give it 10–15 minutes to cool down before reaching inside.
Required Tools
You likely already have everything you need in a basic home toolkit.
- Nut Driver or Screwdriver: Most furnace panels and ignitor brackets are held in place by 1/4" or 5/16" hex-head screws. A multi-bit screwdriver is usually sufficient.
- Work Gloves: Use these for protection while opening the metal cabinet, which can have sharp "burred" edges.
- Flashlight: The interior of a furnace cabinet is notoriously dark; a headlamp is even better, so you can keep your hands free.
Handling the New Ignitor: The Golden Rule
This is the most critical part of your preparation: Never touch the black or gray element of the new ignitor with your bare hands.
Why? Your skin carries natural oils. If these oils get on the ignitor element, they create a "hot spot" when the part heats up to its operating temperature (which can exceed 2,500°F). This causes the ceramic to crack, meaning your brand-new part will burn out in a matter of days—or even minutes.
Pro Tip: Keep the new ignitor in its protective foam or packaging until the exact moment you are ready to slide it into the furnace.
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Step-by-Step Replacement Guide
With your tools ready and the power disconnected, it’s time to get to work. Replacing the ignitor usually takes less than 20 minutes from start to finish. Follow these steps carefully to ensure a successful install.
Step 1: Remove the Access Panels
Most furnaces have two panels: the upper one covers the blower and the lower one covers the burner assembly. Slide or unscrew the panel covering the burner box—this is where the gas valves and the ignitor are located. Set the screws aside in a cup so they don’t roll away.
Step 2: Locate and Unplug the Wire Harness
Trace the wires leading from the ignitor back to the control board or a plastic plug. Do not pull on the wires themselves; instead, squeeze the plastic locking tabs on the harness and gently pull it apart.
Step 3: Remove the Mounting Screw
The ignitor is typically held in place by a single screw on a small metal bracket.
- Be Careful: Use one hand to steady the ignitor while you unscrew the bracket with the other.
- The "Old Part" Check: Once the screw is out, carefully slide the old ignitor out of its slot. Even if it’s broken, handle it gently so you don’t drop ceramic shards into the burner.
Step 4: Compare the Old and New Parts
Before you unwrap the new ignitor, hold it next to the old one (still in its packaging if possible).
- Ensure the plug matches the furnace harness.
- Ensure the bracket is the same shape.
Many replacement kits come with multiple brackets; choose the one that matches your original.
Step 5: Install the New Ignitor
Slide the new ignitor into the burner box slot. Ensure the element doesn't bump against the metal sides of the burner, as the ceramic is extremely brittle.
- Line up the bracket hole with the screw hole.
- Hand-tighten the screw first, then finish with your driver.
Do not overtighten, as the pressure can crack the ceramic base.
Step 6: Plug in the Harness and Close Up
Snap the plastic wire harness back together until you hear it "click." Reattach the furnace access panels. Most furnaces have a "door switch" that prevents the unit from turning on if the panels aren't seated perfectly.
Step 7: Turn on Your Furnace
- Turn the Gas Valve back to the "ON" position.
- Flip the Service Switch or breaker back to "ON."
- Set your thermostat to "Heat" and crank the temperature up.
Watch the sequence: You should hear the inducer fan start, followed shortly by a bright orange glow, and finally, the "whoosh" of the burners igniting.
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Troubleshooting Common Failures
If your furnace still isn't firing up, or if your brand-new ignitor fails shortly after installation, don’t panic. There are a few common causes that can interfere with the process.
Identifying these can help you decide if you need a different part or if there is an underlying issue killing your ignitors prematurely.
The Ignitor Glows, but the Gas Doesn't Light
If you see that beautiful orange glow but the burners never catch fire, the ignitor likely did its job, but the gas isn't reaching it.
- Check the Gas Valve: Double-check that you turned the gas back to the "ON" position.
- Safety Lockout: If the furnace tried to light too many times unsuccessfully, the control board might be in "hard lockout."
Turn the power off at the service switch for 60 seconds to reset the logic board.
The Ignitor "Short-Cycles" (Fails Quickly)
If you find yourself replacing the ignitor every single winter, something is wrong.
Dirty Air Filters:
When your filter is clogged, the furnace runs hotter and more frequently. This extra "cycling" puts unnecessary stress on the ignitor, causing it to burn out years before its time.
Skin Oil Contamination:
As mentioned earlier, even a single fingerprint on the element can cause it to shatter under heat. Always use gloves or handle the part by the ceramic base only.
Moisture and Condensation
High-efficiency (90%+) furnaces produce condensation. If your drain lines are backed up, water can drip onto the hot ignitor. Since the ignitor is ceramic, the thermal shock of cold water hitting a 2,500°F surface will cause it to crack instantly.
Look for water stains inside the burner cabinet.
Wrong Voltage or Part Number
Not all ignitors are created equal. Some operate at 80V, while others operate at 120V.
If you put a 120V "universal" ignitor into a furnace designed for 80V, it may never get hot enough to light the gas.
Conversely, putting an 80V ignitor into a 120V system will cause it to flash brightly and burn out immediately. Always check your furnace’s model number against the ignitor’s compatibility list.
The Flame Sensor Issue
Sometimes the furnace lights for 3 to 5 seconds and then shuts off.
This is usually a dirty flame sensor, not a bad ignitor. The ignitor did its job, but the furnace doesn't "see" the flame and shuts down for safety. Cleaning the sensor with a bit of steel wool is often the fix.
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