Furnace Hot Surface Igniter Replacement

A failed hot surface igniter is the single most common cause of a furnace that tries to start but won’t produce heat. The igniter glows to ignition temperature, typically 1,800–2,500°F, to light the gas burner on every heating cycle. After 3–7 years of daily thermal stress, they crack or fail. Replacing one is a straightforward repair that most homeowners can complete in under 45 minutes, and the part costs $15–$50 in most cases.

This guide covers how to confirm the igniter is the problem, how to select the right replacement, and the exact installation procedure.

What Does a Hot Surface Igniter Do?

Modern furnaces replaced standing pilot lights with hot surface igniters in the late 1980s. On a call for heat, the control board powers the igniter for 17–30 seconds (the warm-up period), then opens the gas valve. If the igniter is working, the gas immediately lights and the flame sensor confirms a flame to the board.

Two types are in common use:

Silicon carbide (SiC) igniters, Older design, used in furnaces built through the mid-2000s. These are gray and fragile, they crack if touched with bare hands (skin oil causes thermal cracking). Resistance at room temperature: 40–70 ohms.

Silicon nitride (Si3N4) igniters, Newer design, used in most furnaces built after 2005. These are darker and more mechanically durable. More resistant to thermal cycling. Resistance at room temperature: 15–75 ohms depending on wattage.

Both types fail either by cracking (visible crack in the element) or by gradual resistance increase until they no longer glow hot enough to ignite gas.

How to Fix It

How to Confirm the Igniter Is the Problem

Don’t replace the igniter until you’ve confirmed it’s actually faulty. A flame sensor failure and an igniter failure produce nearly identical symptoms, the furnace fires up, you see no flame, and the board shuts down.

Visual Inspection

1. Cut power to the furnace at the breaker.
2. Locate the igniter inside the burner compartment, it’s positioned above or beside the burner assembly, directly in the gas stream.
3. Look for visible cracks in the igniter element. A cracked igniter is definitely bad.
4. Also check the igniter wire harness, a broken wire can prevent power from reaching a perfectly good igniter.

Resistance Test (Most Reliable)

1. Disconnect the igniter’s two-pin wire connector.
2. Set your multimeter to the ohms (Ω) range.
3. Touch probes to both pins of the igniter connector.
4. Silicon carbide: 40–70 ohms = good. Out of range = replace.
5. Silicon nitride: 15–75 ohms = good. Out of range = replace.
6. Infinite (OL) resistance = open element, definitely replace.
7. Zero resistance = shorted element, replace.

Live Voltage Test (Confirms Board Output)

If the resistance tests good but the furnace still won’t light:

1. Restore power and set the thermostat to call for heat.
2. Do not put hands near the gas valve area while power is live.
3. Using a multimeter on AC voltage, measure across the igniter terminals during the warm-up period (the 17–30 second window before the gas valve opens).
4. You should see approximately 120VAC (some igniters use 24V, check your spec).
5. No voltage = board not sending power = control board or wiring issue, not the igniter.

How to Size Your Replacement Igniter

The igniter must match your furnace make, model, and wattage rating. Using the wrong wattage causes either insufficient glow temperature (won’t light) or overheating (premature failure).

Finding your igniter specs:

1. Furnace model number, Located on a label inside the furnace cabinet, usually on the front or blower compartment door. Write this down before ordering.
2. Igniter part number, Often printed on the ceramic base of the igniter.
3. Cross-reference tables, Major igniter manufacturers (White-Rodgers, Emerson, Packard, Supco) publish cross-reference tables that map furnace model numbers to compatible igniters.
4. Universal igniters, Universal silicon nitride igniters (like the White-Rodgers H06E series or Supco IGN3) come with multiple mounting brackets and work with hundreds of furnace models. These are a safe choice when you need a same-day fix and can’t wait for an OEM part.

Common OEM igniter wattages by furnace brand:

• Carrier/Bryant: 120V, 80W silicon nitride
• Lennox: 120V, 80W silicon nitride (newer) or 120V, 45W silicon carbide (older)
• Trane/American Standard: 120V, 80W silicon nitride
• Goodman/Amana: 120V, 80W silicon nitride
• Rheem/Ruud: 120V, 80W silicon nitride
• Older units (pre-2005): 120V, 45W silicon carbide

Step-by-Step Replacement Procedure

Tools Needed

• 5/16” nut driver or socket
• #2 Phillips screwdriver
• Multimeter
• Needle-nose pliers
• Thin gloves (for silicon nitride igniters, gloves are optional but good practice; silicon carbide absolutely requires no skin contact)

Installation Steps

Step 1: Cut all power. Turn off the furnace at the thermostat. Flip the circuit breaker for the furnace. Also cut the power switch mounted on or near the furnace (the switch that looks like a light switch) if present.

Step 2: Allow the furnace to cool if it recently ran. Igniters hold heat for several minutes after operation.

Step 3: Access the burner compartment. Remove the lower access panel (usually two screws or a lift-and-pull clip). Some furnaces have a secondary inner panel, remove that too.

Step 4: Locate the igniter. The igniter is mounted to a ceramic or metal bracket, positioned above, alongside, or slightly upstream of the burner assembly. The element protrudes into or near the main burner port.

Step 5: Photograph the igniter location and wiring. Before removing anything, take a photo showing the igniter orientation and how the wire harness is routed. The replacement must be installed in the same orientation.

Step 6: Disconnect the wire harness. The igniter connects via a two-pin quick-disconnect plug. Pull it straight apart, do not pry from the connector side.

Step 7: Remove the igniter mounting screws. Most igniters are held with one or two 5/16” hex-head screws through a ceramic mounting bracket. Remove them carefully and set aside.

Step 8: Remove the old igniter. Slide it out carefully. Note the orientation of the element relative to the burner ports.

Step 9: Handle the new igniter correctly.

• Silicon nitride: can be touched by clean hands, but gripping by the ceramic base is safest.
• Silicon carbide: do not touch the element with bare skin. Hold only by the wire leads or wear gloves. Skin oils cause stress fractures during the first heat cycle.

Step 10: Install the new igniter. Position it in the same orientation as the old one. The element should point toward the main burner port, it should be close to but not touching the burner.

Step 11: Secure mounting screws. Finger-tight plus 1/4 turn, do not overtighten ceramic mounting brackets.

Step 12: Reconnect the wire harness. Push the connector together until it clicks.

Step 13: Reassemble panels and restore power. Replace both access panels, restore the circuit breaker and furnace switch, and set the thermostat to call for heat.

Step 14: Watch the startup cycle. The igniter should begin glowing orange-hot within 20 seconds of the call for heat. Gas should light within 30 seconds. If the unit fires and runs normally, the repair is complete.

Parts You May Need

Need replacement parts? Search for parts and tools on Amazon.

When to Call a Pro

Handle yourself: Visual inspection, resistance test, igniter replacement, flame sensor cleaning.

Call a technician if:

• The new igniter glows but gas still won’t light. Possible causes: gas supply issue, gas valve fault, pressure switch not proving, or inducer not creating adequate draft. These require further diagnosis beyond igniter replacement.
• The furnace goes into lockout immediately after the igniter fires. The flame sensor is the likely culprit, try cleaning it before calling (fine steel wool on the sensor rod), but if cleaning doesn’t help, the sensor, wiring, or control board needs evaluation.
• The igniter shows good resistance but the board isn’t sending 120V. This is a control board or wiring fault.
• Any smell of gas without ignition. Shut the gas off, ventilate the home, and call a technician. Do not attempt to restart.

FAQ

How do I know if my igniter is silicon carbide or silicon nitride? Silicon carbide igniters are typically gray and more brittle-looking; they read 40–70 ohms at room temperature. Silicon nitride igniters are darker (often grayish-black) and more robust; they read 15–75 ohms. If you’re unsure, look up your furnace model in an igniter cross-reference table, it will specify which type is required.

My new igniter glows but not as bright orange as expected. Is it defective? Silicon nitride igniters glow at a lower visible temperature than silicon carbide, they’ll look more of a dull orange-red than the bright orange of a silicon carbide igniter. This is normal for silicon nitride. What matters is that the element reaches the correct surface temperature (typically around 2,200°F), not the visible color intensity.

Can I reuse the mounting screws from the old igniter? Usually yes, the 5/16” hex screws are generic and reusable. If they’re stripped or corroded, hardware stores carry the correct size, or you can use the screws included with a universal igniter kit.

How long should a new igniter last? A quality OEM or name-brand universal igniter (White-Rodgers, Honeywell, Supco) typically lasts 3–7 years under normal residential use. Cheap no-name igniters sold on discount sites sometimes fail within a heating season. Don’t cheap out on this part, the $10 savings isn’t worth another service visit.

The furnace ran fine for months after I replaced the igniter, then stopped again. Same symptom. Why? First, retest the new igniter, they do occasionally fail early. If the igniter tests good, the flame sensor is the next thing to check. A dirty or failing flame sensor can cause the same symptoms, the igniter lights the gas, but the sensor can’t confirm the flame, so the board shuts the gas off after a few seconds. Clean the flame sensor rod with steel wool before replacing it.

Technician Tips

Igniter failures are model-specific. Match the mounting bracket, ceramic length, connector, and voltage before ordering, then verify the flame sensor and gas valve sequence if the furnace still drops out after the new igniter glows.

Parts note: The most common parts to price with an igniter repair are the matching hot-surface igniter, flame sensor rod, rollout or limit switch, and pressure-switch tubing. Do not swap the control board until the ignition sequence and safety circuit have been tested.