Pilot Light on Furnace Keeps Going Out? Fix It Now
- shawncovenantaire
- Oct 9
- 14 min read
When your furnace pilot light keeps going out, it's almost always pointing to one of two things: a faulty thermocouple or a dirty pilot orifice. These parts are critical for your furnace to run safely. When one of them acts up, your furnace does exactly what it's supposed to do; it shuts down as a safety precaution.
Figuring out which one is the culprit is the first step to getting your heat back on.
Diagnosing a Failing Pilot Light
A pilot light that refuses to stay lit is more than just an annoyance on a cold day. It's a clear signal from your furnace that a key component needs your attention. Before you can even think about a fix, you need to understand what's happening behind that little furnace panel.
The whole system is designed with safety as the top priority. So, when the pilot flame dies, it’s usually because a safety mechanism has done its job.
Your furnace is essentially a controlled combustion process. Two key players keep this process safe and effective: the thermocouple and the pilot orifice. You can think of the thermocouple as the safety sensor and the pilot orifice as the tiny fuel jet. If either one isn't doing its job right, the whole system grinds to a halt.
This infographic gives a quick visual rundown of how to approach a pilot light that keeps going out.
As you can see, the diagnostic journey starts with a simple observation of the flame and then moves on to inspecting specific parts like the thermocouple.
Key Components to Check
When your pilot light won't stay lit, your investigation should zero in on these two primary suspects. Each one has a distinct job in keeping that flame alive and your furnace running.
The Thermocouple: This is a safety device that sits directly in the pilot flame. Its job is to sense the heat and send a tiny electrical current to the gas valve, telling it, "It's safe, stay open." If the thermocouple is dirty, bent out of position, or just plain worn out, it can't generate that signal, and the gas valve snaps shut. No gas, no flame.
The Pilot Orifice: This is a minuscule opening that delivers a steady, precise stream of gas to the pilot light. Over time, it can get clogged with dust, soot, or other debris. Even a partial clog will result in a weak, flickering, or yellow flame that just isn't hot enough to properly heat the thermocouple.
To quickly tell these issues apart, here’s a table outlining the common problems, what you'll likely see, and whether it's something you might tackle yourself.
Common Causes of Pilot Light Failure
This table should help you narrow down the possibilities before you start taking things apart.
Initial Diagnostic Steps
You can often pinpoint the likely cause with a simple visual check. Get a good look at the pilot flame itself. Is it a steady, strong blue color, or is it weak, flickering, and maybe a little yellow or orange?
A healthy pilot flame should be a crisp, steady blue, engulfing the top third of the thermocouple. A weak, yellow, or wavering flame often indicates a dirty pilot orifice or a gas supply issue, preventing the thermocouple from getting hot enough to function.
So, if the flame looks weak and lazy, the problem is probably a dirty orifice. If the flame looks strong and blue but still goes out a few minutes after you let go of the button, the thermocouple is the more likely culprit.
While some of these issues can be fixed with careful cleaning, diagnosing and replacing parts can get tricky and often requires professional know-how. For more complex problems, looking into your options for professional gas furnace repair is the best next step for a safe and permanent solution.
The Thermocouple: Your Furnace's Safety Switch
You can think of the thermocouple as your furnace's silent, vigilant bodyguard. It’s a small, metallic rod with its tip sitting right in the pilot flame, and it has one critical job: to confirm the pilot is lit before allowing gas to flow to the main burners. It's a simple yet brilliant safety device.
When that tiny pilot flame heats the thermocouple's tip, it generates a small electrical charge, just a few millivolts. This current travels down a copper tube and sends a signal to the main gas valve, essentially saying, "All clear, the flame is active, you can stay open." It’s the gatekeeper that prevents raw, unburned gas from filling your home.
But like any part that endures constant heat, thermocouples don't last forever. After years of service, they can get dirty, degrade, or simply wear out. When that happens, they can no longer produce the electrical signal needed to hold the gas valve open, causing the pilot light on your furnace to keep going out.
Signs of a Failing Thermocouple
A faulty thermocouple is one of the most common culprits when a pilot light won't stay lit, and the symptoms are usually pretty specific. You’ll notice the pilot light ignites just fine and burns with a strong, blue flame as long as you hold the gas knob down.
The moment you let go, though, poof, the flame extinguishes. This is the classic calling card of a thermocouple that has given up the ghost. A healthy one needs about 30 to 60 seconds in the flame to generate enough power. If it can't hold the charge after that, something's wrong.
Common issues I see all the time include:
Soot or Carbon Buildup: A layer of black soot can act like an insulator on the tip, preventing it from getting hot enough to work correctly.
Incorrect Positioning: If the thermocouple has been bumped or bent, it might not be properly engulfed by the pilot flame. The tip needs to sit in the hottest part of the flame, which is typically the upper third.
Physical Damage: Give the copper line a quick look for any cracks, corrosion, or kinks. Any physical damage can interrupt that tiny electrical signal.
In fact, a faulty thermocouple is estimated to account for up to 30% of all pilot light problems in older gas furnaces. As this component degrades, its voltage drops, causing the gas supply to shut off even when the flame is still burning. With about 15% of gas furnaces in U.S. homes being over 20 years old, thermocouple failures are a common reason for service calls each winter.
How to Test a Thermocouple
If you want a definitive diagnosis, you can test the thermocouple's output with a digital multimeter. It's a straightforward process that will tell you for sure if the part is producing the necessary voltage. A healthy, functioning thermocouple should generate between 20 and 30 millivolts (mV). Anything significantly lower, especially a reading under 18 mV, usually isn't enough juice to hold the gas valve open.
If your tests confirm the thermocouple is the problem, the good news is that it’s an inexpensive part to replace. While the component itself is affordable, keeping the entire system in good shape is the real key to preventing future failures. For a deeper dive into preventative care, you can learn more about proper gas furnace maintenance to keep your whole system running smoothly.
What to Check After the Thermocouple
So, you've confirmed your thermocouple is in good working order, but that stubborn pilot light just won't stay lit. What's next? It's time to dig a little deeper and look at the fundamentals: fuel and air. A healthy pilot flame needs a steady, uninterrupted supply of both to survive.
Even a pilot light that looks like a strong blue flame can be deceiving. If the flame is unstable because of a draft or an issue with the pilot assembly, it can flicker out in an instant. When that happens, the thermocouple does its job and shuts the gas off. Let's walk through some of these less obvious, but very common, reasons your furnace is giving you trouble.
A Clogged Pilot Orifice
Think of the pilot orifice as the nozzle on a tiny fuel injector. It's a pinhole-sized opening that creates a very precise stream of gas for the pilot flame. Because this opening is so minuscule, it doesn't take much to clog it up with dust, soot, or mineral deposits left behind by a nearby humidifier.
When the orifice gets partially blocked, the gas flow becomes restricted. This essentially starves the pilot flame, making it weak, yellow, and lazy. An anemic flame like that often can't generate enough heat to keep the thermocouple engaged, which is another common reason the pilot light on your furnace keeps going out.
A healthy pilot flame should be a strong, steady blue cone that wraps around the top third of the thermocouple. If yours looks more like a flickering, small, or yellow flame, that's a classic sign the pilot orifice needs a good cleaning.
To clean it safely, you'll need to shut off the gas, remove the pilot assembly, and use a very thin wire or a blast of compressed air to clear out the blockage. This small bit of maintenance can make a world of difference.
The Problem with Drafts
Your furnace room might seem perfectly still, but it only takes a subtle air current to blow out that delicate pilot flame. These sneaky drafts can pop up from some pretty unexpected places, turning your furnace area into a mini wind tunnel.
Common sources of drafts include:
Cracks in Windows or Foundations: Even tiny gaps in basement windows or the foundation can let in surprisingly strong gusts of cold air.
Nearby Vents: Is your clothes dryer vent or a return air vent located too close to the furnace? The air movement can be enough to disrupt the pilot.
The Furnace Blower Itself: In some cases, a crack in the heat exchanger can cause air from the main blower to leak into the burner compartment, extinguishing the flame.
A simple way to test for this is to just watch the pilot flame. Does it dance or flicker, especially when the main blower kicks on or on a windy day? Sealing up those drafts is often an easy, permanent fix. Sometimes, this can also point to a bigger issue, like when your furnace cycles on and off frequently, which creates its own airflow problems. If that sounds familiar, you can learn more about why your furnace cycles on and off frequently and find some easy fixes in our other guide.
Issues with the Main Gas Valve
If you've checked the thermocouple, cleaned the orifice, and sealed any drafts, the issue might be with the main gas valve or regulator. This component is the command center for your furnace's gas system, controlling the flow to both the pilot and the main burners.
Over time, these valves can start to fail internally. The internal diaphragm might weaken or the electronics can wear out, causing inconsistent gas pressure. The symptoms can be subtle at first; maybe just a flame that seems a bit weaker than it should. A failing gas valve is a more complex and serious problem that, for safety's sake, almost always requires a professional diagnosis from a certified HVAC technician.
Your Safety Checklist Before You Begin
Alright, before you grab a single tool, let's hit pause. Working on a gas furnace isn't like unclogging a drain. We're dealing with natural gas, flames, and fumes, which means your safety is the #1 priority. Getting this wrong can have serious consequences, so this safety check is the most critical part of the whole job.
First things first: shut off the gas supply to the furnace. Look for the gas pipe leading into the unit; you should find a valve, usually with a red or yellow handle. Give it a quarter-turn so the handle is perpendicular to the pipe. That's it. The gas is now off.
Next up, kill the power. Head over to your home's main circuit breaker panel and flip the switch for the furnace. This makes sure the unit doesn't unexpectedly try to fire up while you're working on it.
Ventilation and Gas Leak Detection
With the gas and power safely off, it's time to think about fresh air. Open a window or door near the furnace to get some air circulating. It’s a simple but vital step to help clear out any lingering gas and prevent any potential buildup.
Now, let's do a quick but essential gas leak check. Your nose is your first line of defense; natural gas has that distinct "rotten egg" smell added for exactly this reason. If you smell gas, stop everything immediately. Leave the area and call your gas company from a safe distance.
For a more thorough check, you can use the classic soap and water trick:
Mix a little dish soap with water in a spray bottle.
Lightly spray the solution on the gas fittings and connections around the pilot assembly.
If you see any bubbles forming, that means you have a gas leak. This isn't a DIY fix; it requires a professional right away.
Working with natural gas always carries the risk of carbon monoxide (CO) exposure if combustion is incomplete. Given the nature of gas furnaces, familiarizing yourself with crucial information on carbon monoxide safety is an absolute must before attempting any work.
Know Your Limits
This safety checklist is the bare minimum for anyone thinking about tackling a furnace issue themselves. If at any point you feel like you're in over your head, or if you find a problem like a gas leak or significant corrosion, it's time to put the tools down and call a pro.
Staying on top of routine checks is also a huge part of staying safe. Following an HVAC preventative maintenance checklist can help you catch these kinds of safety issues before they turn into full-blown emergencies. Always remember: your safety and the safety of your home come first. No exceptions.
Knowing When to Call an HVAC Professional
Look, I'm all for a good DIY fix. Many pilot light issues are things you can absolutely handle yourself. But there's a fine line between a simple repair and a symptom of a much bigger, more dangerous problem. Knowing when to put down the tools and pick up the phone isn't admitting defeat, it's just being smart and safe.
There are a few red flags that should immediately stop you in your tracks. These aren't suggestions; they're clear signs that you're dealing with something beyond a simple adjustment and need an expert eye on it.
Clear Signs to Stop and Call a Pro
If you run into any of these situations, it's time to call a professional. Trying to push through these problems on your own can be incredibly dangerous and often leads to much more expensive damage.
You Smell Gas: This is the big one. If you catch that distinct "rotten egg" smell, even after the pilot is out and you've shut the gas off, you could have a leak in the gas line itself. Don't try to be a hero and find it. Get out of the house, call your gas company, and then call an HVAC technician right away.
Significant Rust or Corrosion: A bit of surface rust is pretty normal on an older unit. But if you see heavy, flaky corrosion on the burner assembly, gas lines, or especially the heat exchanger, that's a serious problem. Corroded parts can fail without any warning, leading to gas leaks or other unsafe conditions.
A Yellow, Sooty Pilot Flame: While a weak, slightly yellow flame can just mean a dirty orifice, a large, lazy, or sooty yellow flame is a major warning. This can be a sign of a cracked heat exchanger, which is a severe safety hazard that could leak carbon monoxide into your home. Don't mess with this.
The Furnace is Constantly Short Cycling: Is the pilot light problem happening at the same time the furnace is kicking on and off every few minutes? That points to a much more complex issue. It could be anything from a failing control board to a serious airflow blockage that you just can't diagnose without professional tools.
A professional diagnosis is almost always cheaper in the long run. An experienced tech can pinpoint the real source of the problem in minutes, making sure the right part gets replaced and preventing a frustrating cycle of failed DIY fixes that could damage other components.
The Long-Term Value of an Expert Opinion
Sometimes, a pilot light that keeps going out is your furnace's way of telling you its time is almost up. An HVAC professional isn't just going to glance at the pilot light; they're going to assess the health of the entire system.
They can give you the honest truth: will a simple repair get you through another winter, or are you just throwing good money at a failing unit? For homeowners stuck in that spot, understanding the key signs it might be time to replace your furnace can save you a fortune. Getting an expert opinion ensures your system is running safely and efficiently, giving you peace of mind that a small fix won’t spiral into a costly and hazardous mistake.
Got Questions About Your Furnace Pilot Light? Here Are Some Answers
When your furnace pilot light decides to take an unscheduled vacation, it can be a real headache. It also brings up a lot of questions. Let's walk through some of the most common concerns homeowners have when they're staring at a pilot light that just won't stay lit.
How Much Is This Going to Cost Me?
The final bill can swing pretty wildly depending on what's actually wrong. Sometimes, you get lucky. A simple fix, like carefully cleaning out a clogged pilot orifice, might not cost you a penny beyond your own time.
If you need to call in a pro, the usual suspect is a bad thermocouple. Getting that replaced is a common job and will likely run you somewhere between $100 and $250. However, if the issue is deeper, say, a failing gas valve or a fried control module, the price tag can jump significantly, often landing in the $300 to $700 range. Always get a clear, itemized quote before you give a technician the green light to start working.
Is It Dangerous If My Pilot Light Keeps Going Out?
For the most part, no, it's not an immediate, life-threatening danger. Your furnace has a built-in safety feature, that same thermocouple we just talked about, whose entire job is to shut off the gas supply if the pilot flame extinguishes. This is specifically designed to stop raw gas from seeping into your home.
The situation becomes dangerous if that safety system fails or if you smell gas. If you ever catch that distinct "rotten egg" smell, that's your cue to leave the house immediately. Don't touch light switches, don't use your phone, just get outside. Once you're a safe distance away, call your gas company. In most cases, the biggest risk is simply being without heat, which can become a serious problem in the dead of winter.
Can I Just Relight the Pilot Light Myself?
Absolutely. If you have an older furnace with a standing pilot light, relighting it is usually a straightforward DIY task. You'll almost always find a sticker with step-by-step instructions right inside the furnace's front access panel.
While you should always follow your manufacturer's directions, the process generally looks something like this:
Find the gas control knob and turn it to the "PILOT" setting.
Press and hold that knob down. This starts the flow of gas to the pilot assembly.
Use a long lighter or match to ignite the gas stream.
Keep holding the knob down for up to 60 seconds. This gives the thermocouple time to heat up and signal that the flame is lit.
Slowly let go of the knob. If the flame stays on, turn the knob to the "ON" position, and you're back in business.
Do New Furnaces Even Have Pilot Lights?
Not anymore, for the most part. The vast majority of modern, high-efficiency furnaces have ditched the old-school standing pilot light. They now use electronic ignition systems, like hot surface ignitors or intermittent pilots.
These systems are way more energy-efficient because they only ignite the gas at the exact moment your thermostat calls for heat. This change completely eliminates the classic "pilot light won't stay lit" problem and cuts down on wasted energy. An old, continuously burning pilot light can burn through 400 to 1,200 cubic feet of natural gas every month, even when your furnace isn't running. That's a lot of wasted money. To keep your system in top shape and avoid these kinds of recurring headaches, it's always a good idea to follow an ultimate HVAC preventive maintenance checklist.
When furnace troubles go beyond a simple question, you need a reliable partner to restore your home's comfort and safety. The certified technicians at Covenant Aire Solutions are available 24/7 to diagnose and fix any issue, from a stubborn pilot light to a complete system failure. For honest, expert service in Tucson and the surrounding areas, visit us at covenantairesolutions.com.