It is 3:00 AM. The house feels like an icebox, and you're standing in a cold basement staring at a rusted metal box that’s supposed to be keeping your family warm. You hear the click-click-click of the igniter, but nothing happens. No "whoosh" of heat. Just silence. Most homeowners panic and call a technician for $200 before realizing the solution is literally a single match and sixty seconds of patience. Honestly, learning how to light a pilot light on a furnace is one of those basic "adulting" skills that saves you a fortune over a lifetime.
Old furnaces are stubborn. Modern high-efficiency models don't even have standing pilots—they use electronic ignition—but millions of homes across North America still rely on that tiny, flickering blue flame to bridge the gap between "freezing" and "functional." If you have a furnace manufactured before the mid-90s, you likely have a standing pilot. It’s a simple mechanical system, but it’s also temperamental. If the wind blows too hard down the flue or if a speck of dust settles in the wrong place, the flame dies. Then, the thermocouple—a safety device—shuts off the gas flow to prevent your house from turning into a giant tinderbox.
The Step-by-Step Reality of Lighting Your Furnace
First, safety. If you smell gas—that distinct, rotten-egg sulfur stench—stop reading this. Get out of the house. Do not flip a light switch. Do not use your phone inside. Call the gas company from the curb. But if there’s no smell and just a cold house, you’re probably fine to proceed.
Locate the gas valve. It’s usually a round knob with three settings: ON, OFF, and PILOT. You’ll need a long-reach grill lighter or a very long fireplace match. Don't try this with a standard Bic lighter unless you enjoy losing your knuckle hair. Turn the knob to OFF and wait at least five full minutes. This isn't a suggestion; it’s a requirement. You need any residual gas to dissipate before you introduce a flame.
- Turn the knob to the PILOT setting.
- Find the pilot orifice. It’s usually at the end of a small silver tube leading toward the burner assembly.
- While holding your lighter flame at the tip of the pilot, press and hold the reset button (usually the knob itself or a separate red button nearby).
- Watch for the blue flame to catch.
- Keep holding that button down for at least 30 to 60 seconds.
Why the wait? You’re waiting for the thermocouple to get hot. This little copper rod generates a tiny millivolt electrical signal when heated, which tells the gas valve it’s safe to keep the gas flowing. If you let go too early, the flame will just blink out. Once you let go and the flame stays lit, slowly turn the knob to the ON position. You should hear the main burners roar to life shortly after.
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What Happens When the Flame Won't Stay Lit?
If you followed those steps and the flame died the second you let go of the button, you’re likely dealing with a dirty or failing thermocouple. This is the #1 cause of furnace service calls in the winter. Over time, carbon soot builds up on the copper rod, insulating it from the heat. The valve "thinks" the pilot is out, so it kills the gas.
Sometimes you can fix this with a piece of fine-grit sandpaper or a stiff toothbrush. Just a light scrubbing to reveal the bright copper can be enough to get the signal flowing again. But if the thermocouple is actually burnt out, you can’t "fix" it. You have to replace it. The good news? They cost about $15 at any hardware store like Home Depot or Lowe’s. Replacing one is a bit of a "knees-on-the-cold-concrete" job, involving a small wrench and some patience, but it’s infinitely cheaper than a midnight service call.
The Different Types of Ignition Systems
It's actually pretty common for people to spend twenty minutes looking for a pilot light that doesn't exist. If your furnace was built in the last 20 years, you probably have Electronic Ignition.
There are two main types here:
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- Intermittent Pilot: This uses an electric spark to light a pilot only when the thermostat calls for heat. Once the burners are on, the pilot stays lit, but then it shuts off once the cycle is done. It saves gas because you aren't burning a flame 24/7.
- Hot Surface Ignition (HSI): This is the most common modern setup. It uses an igniter that looks like a little car cigarette lighter. It glows bright orange until it’s hot enough to ignite the gas. These are notorious for cracking. If you see the igniter glowing but no fire happens, the gas valve might be stuck, or the igniter might be just weak enough to fail under pressure.
If you have one of these systems, you won't find a "Pilot" knob. You’ll just have an ON/OFF switch. In these cases, "lighting the pilot" isn't an option. You usually have to reset the furnace by flipping the power switch (looks like a light switch on the side of the unit) or the circuit breaker, waiting a minute, and turning it back on.
Common Misconceptions About Gas Safety
People are terrified of gas. Rightfully so. But the "standing pilot" system is remarkably robust in its failure mode. It is designed to fail "closed." If the pilot goes out, the thermocouple cools down, the electromagnet inside the valve loses its grip, and a spring snaps the gas line shut. The "explosion" risk from a pilot light going out is actually much lower than people think, provided you don't keep manually pumping gas into the chamber without a flame.
Another myth is that you should always leave your pilot lit all summer. Some argue it keeps the heat exchanger dry and prevents spiders from spinning webs in the small gas tubes (spiders actually love the smell of the mercaptan added to gas). Others say it’s a waste of $5–$10 a month in gas. Honestly, if your basement is damp, leave it on. If it's bone dry, shut it off in May and save the cash.
Troubleshooting the "Ghost" Pilot
If you know how to light a pilot light on a furnace but the flame is orange and flickering rather than a crisp blue, you have an oxygen problem. A healthy pilot looks like a small blowtorch—steady, blue, with maybe a tiny yellow tip. An orange, lazy flame means the burner is dirty or there isn't enough combustion air. This can lead to carbon monoxide buildup.
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Check the air intake. Sometimes lint or even a bird's nest in the intake pipe outside can starve the furnace of the air it needs. If the flame is "lifting" off the burner, your gas pressure might be too high. This isn't a DIY fix. You need a manometer to check gas pressure, and that’s firmly in the territory of a licensed HVAC pro.
Real-World Statistics on Furnace Failures
According to data from the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), nearly 25% of all emergency heating calls in older homes are related to pilot light or thermocouple issues. In many cases, the "broken" furnace is just a victim of a drafty basement. If your furnace is located near a drafty door or a window that doesn't seal, a strong gust can literally blow the pilot out. If this happens repeatedly, consider installing a pilot light shield or simply sealing the drafts in the room.
Practical Next Steps for the Homeowner
If you've managed to get the flame back on, don't just walk away and forget about it. This is your warning shot.
- Buy a spare thermocouple today. Keep it taped to the side of the furnace. When it fails for real at 10 PM on a Sunday, you’ll be the hero.
- Check your carbon monoxide (CO) detectors. Every time you mess with the furnace, test the detectors. A pilot light issue can sometimes be a precursor to venting problems.
- Clean the area. Vacuum the dust and pet hair from around the base of the furnace. Dust is fuel for a small flame and a major contributor to clogged pilot tubes.
- Schedule an annual tune-up. Even if you lit it yourself, an old furnace needs a pro to check for cracks in the heat exchanger. That's the one thing you can't see, and it's the one thing that can be deadly.
If you’ve tried lighting it three times and it won't stay, stop. You might have a bad gas valve or a cracked line. It sucks to pay for a service call, but it's cheaper than a new house. Most techs can swap a thermocouple and clean your pilot assembly in under an hour. Keep the contact info for a local, reputable HVAC company written on the side of the furnace in permanent marker so you aren't scrambling for your phone when the temperature hits zero.
The Maintenance Checklist
Don't wait for the next cold snap. Go down to the basement tomorrow morning and look at the flame. Is it blue? Is it steady? If it's dancing around, you’ve got work to do. Check the venting pipes for any signs of rust or white powdery residue, which indicates improper drainage or venting issues. Taking five minutes now prevents a three-day headache later when the local repair shops are all booked solid during a blizzard.