How to Check Your Furnace Pilot Light or Igniter
The ignition system is where most "furnace won't heat" problems start. Whether your furnace uses a standing pilot light or an electronic igniter, a quick visual inspection can tell you if this is your issue — and many fixes take less than 15 minutes.
Time Required
10-15 minutes
Difficulty
Medium
Safety
Gas awareness required
Gas Safety Warning
Before working near any gas-burning component, sniff for the rotten egg smell of natural gas. If you detect gas odor, do not flip any switches or use your phone. Leave the house immediately, take your family and pets, and call your gas company from outside. Never attempt to relight a pilot if you smell gas.
Identify Your Ignition Type
The first step is figuring out which ignition system your furnace uses. This determines your entire troubleshooting approach.
- Standing Pilot Light: A small flame burns continuously near the burners. Common on furnaces built before the mid-1990s. You'll see a small gas line running to a pilot assembly.
- Hot Surface Igniter (HSI): A flat, brittle element (often silicon carbide or silicon nitride) that glows orange-hot to ignite the gas. The most common type on modern furnaces.
- Spark Ignition: Uses an electric spark — similar to a gas grill lighter — to ignite a small pilot flame, which then lights the main burners. You'll hear a clicking sound when the furnace starts.
- Direct Spark Ignition (DSI): Sparks directly ignite the main burners without a pilot flame. Less common in residential furnaces but found in some high-efficiency models.
How to Relight a Standing Pilot Light
Turn the gas valve to "Off"
Find the gas control knob on the combination gas valve (usually at the bottom of the furnace). Turn it to the "Off" position. Wait at least 5 full minutes for any residual gas to dissipate before proceeding.
Switch the knob to "Pilot"
After waiting, turn the gas valve knob to the "Pilot" position. This allows gas to flow only to the small pilot assembly, not the main burners.
Press and hold the reset button while lighting
Hold down the pilot button (or push in the gas valve knob, depending on your model) and use a long-reach lighter or the built-in piezo igniter to light the pilot. Keep holding the button for 30-60 seconds after the pilot lights.
Release and check the flame
Slowly release the button. The pilot should stay lit with a steady blue flame that wraps around the thermocouple tip. If it goes out, repeat the process. If it won't stay lit after 3 attempts, the thermocouple likely needs replacing.
Turn the valve to "On"
Once the pilot stays lit, turn the gas valve knob from "Pilot" to "On." Set your thermostat to call for heat and verify the main burners ignite. The pilot flame should turn the burners on within a few seconds.
Troubleshooting Hot Surface Igniters
Hot surface igniters are the most common ignition failure on modern furnaces. They're fragile and have a typical lifespan of 3-7 years.
Locate the igniter
Turn off power to the furnace. Remove the burner access panel. The igniter sits near the burner tubes — a small rectangular or fork-shaped element connected by two wires.
Inspect for cracks
Look closely at the element surface. Even a hairline crack will prevent the igniter from reaching proper temperature. If cracked, it must be replaced — there is no repair.
Clean gently if dirty
If the igniter looks intact but has buildup, gently brush it with a soft-bristle toothbrush. Never use sandpaper, steel wool, or your bare fingers. Oils and abrasives will shorten its life dramatically.
Spark Ignition Troubleshooting
- No clicking sound: The ignition control module may have failed, or power to the furnace could be interrupted. Check the furnace switch and breaker first.
- Clicking but no ignition: The spark electrode may be dirty or positioned too far from the pilot burner. Clean the electrode tip with fine steel wool and verify the gap matches the manufacturer spec (typically 1/8 inch).
- Pilot lights but main burners don't fire: The flame sensor (separate from the spark electrode) may be dirty. Clean it with fine steel wool or emery cloth.
- Intermittent ignition: A cracked porcelain insulator on the spark electrode can cause grounding issues. Inspect the ceramic body for any hairline cracks.
Pro Tips
- •Photograph before you touch anything: Take a photo of the wiring connections and igniter position before removal. This saves time during reinstallation.
- •Buy igniters by model number: Write down your furnace model number (on the rating plate inside the access panel) and order the exact replacement igniter. Universal igniters work but may not last as long.
- •A yellow pilot flame means trouble: A healthy pilot is mostly blue with a small yellow tip. A lazy yellow flame indicates poor combustion — usually a dirty pilot orifice or insufficient air supply.
- •Keep a spare igniter on hand: They cost $15-$40 and fail without warning, always on the coldest night of the year. Having a spare means you can fix it in minutes instead of waiting days for a part or technician.