Diagnose and Replace a Hot Surface Ignitor

If your furnace isn’t producing heat, the hot surface ignitor (HSI) may be the culprit. This crucial component ignites the gas to generate heat, so when it fails, your furnace won’t produce warmth. Replacing an HSI is a DIY-friendly repair with the right tools, proper safety measures, and high-quality parts from Open To Public HVAC Parts. This guide will take you through the entire process.


Step 1: Diagnosing a Faulty Hot Surface Ignitor

The first step is to recognize signs of a failing HSI. Here are some key indicators:

  • No Heat Production: The furnace blower may run, but no warm air is circulated.
  • Frequent Short Cycling: The furnace turns on and off without consistently producing heat.
  • Delayed or Failed Ignition: A “clicking” sound is present, but the furnace doesn’t ignite.
  • Ignitor Not Glowing: When the furnace attempts to start, the ignitor doesn’t produce its characteristic bright orange glow.

If you notice any of these issues, inspect the HSI. Testing the ignitor’s continuity with a multimeter will confirm if it’s the cause. An intact ignitor will typically show between 40 and 200 ohms. If it reads outside this range or shows an “open” circuit, the ignitor likely needs replacement.

Safety Precautions

Before working on your furnace, follow these essential safety steps:

  1. Turn Off Power and Gas Supply:
    • Switch off the furnace’s circuit breaker to avoid electrical shock.
    • Turn off the gas valve by setting it to the “off” position, preventing gas leakage.
  2. Gather Tools and a Compatible Replacement Ignitor:
    • You’ll need a multimeter, screwdriver, socket wrench, and flashlight.
    • Choose a replacement ignitor compatible with your furnace model, available from Open To Public HVAC Parts.

Step 2: Removing the Faulty Ignitor

  1. Open the Furnace Access Panel:
    • Remove the furnace’s front panel, usually secured by screws or clips.
    • Locate the HSI near the burners in the burner assembly.
  2. Inspect the Ignitor for Visible Damage:
    • Look for cracks, chips, or residue, which indicate that the ignitor is worn or has burned out.

Warning: Hot surface ignitors are extremely fragile and should be handled carefully. Avoid touching the silicon nitride or silicon carbide heating element directly, as oils from your skin can damage it. You may handle the ceramic base, but be cautious not to tap or drop the ignitor during removal and installation, as this can lead to cracks or breakage.

  1. Disconnect and Test the Ignitor:
    • Gently disconnect the ignitor’s wiring by pulling on the plastic connector.
    • Set the multimeter to “Ohms” (Ω) and touch the probes to the ignitor’s contacts. A reading outside 40-200 ohms confirms the ignitor needs replacement.

Step 3: Installing the New Ignitor

  1. Position the New Ignitor in Place:
    • Carefully place the new ignitor where the old one was located, ensuring it’s aligned properly without touching the heating element.
  2. Secure the Ignitor:
    • Attach the ignitor to its bracket using the screws, securing it tightly but without over-tightening, which could crack it.
  3. Reconnect the Wiring:
    • Connect the wiring securely to the ignitor, ensuring all connections are tight.

Step 4: Testing the New Ignitor

  1. Restore Power and Gas:
    • Turn on the power and gas supply to restore furnace operation.
  2. Run the Furnace:
    • Set your thermostat to “heat,” triggering the furnace’s ignition cycle. Observe the new ignitor as it glows and ignites the gas.
  3. Confirm Full Operation:
    • Allow the furnace to complete a full cycle, checking for consistent heat production.

Final Steps and Maintenance Tips

After confirming the furnace is working properly:

  1. Turn Off Furnace and Replace the Access Panel:
    • Temporarily turn off the thermostat, replace the access panel, and secure it.
  2. Perform a Final Test:
    • Set the thermostat to heat again, letting the furnace complete a few cycles to confirm consistent operation.
  3. Maintain Your Furnace Ignitor:
    • Keep the ignitor area clean, avoid touching the heating element, and inspect it regularly to catch issues early.

Safety and Liability Notice

Replacing a hot surface ignitor can be a straightforward DIY project, but it involves handling gas and electrical components, which can pose risks if mishandled. If you’re unfamiliar with these systems or feel unsure at any stage, consider consulting a professional to prevent potential safety hazards. Open To Public HVAC Parts is not liable for any damages or injuries sustained during this repair. Always prioritize safety and proceed only if you feel confident in your skills.


With these steps and quality parts from Open To Public HVAC Parts, you can replace your hot surface ignitor safely and get your furnace back up and running efficiently. At Open To Public HVAC Parts, we’re here to support DIYers with reliable parts and resources for all your HVAC repair needs.

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