Furnace Pilot Light Keeps Going Out? Here's What's Wrong
NEXT Heating & Cooling | Published March 2, 2026 | 8 min read
You head down to the basement for the third time this week, lighter in hand, ready to relight your furnace pilot. Again. It's 22 degrees outside in Sterling Heights, and you're tired of this routine. The pilot lights just fine—holds for a few hours, maybe a day—then goes out without warning.
If your furnace pilot light keeps going out, you're dealing with one of five common failures. Most of them are straightforward fixes for an experienced HVAC tech, but a couple signal it's time to consider upgrading your heating system entirely. After 35 years of furnace and AC installation services across Southeast Michigan, we've diagnosed this problem in hundreds of basements—from 1960s ranch homes in Royal Oak to newer builds in Shelby Township.
Here's what's actually going wrong, how to know when you can safely relight it yourself, and when it's time to call a reliable HVAC contractor in Metro Detroit.
What the Pilot Light Actually Does
A pilot light is a small, continuously burning flame that sits near your furnace burners. When your thermostat calls for heat, the gas valve opens and the pilot ignites the main burners. Simple, reliable, old-school technology—which is why furnaces built before the mid-2000s almost all use standing pilots.
The pilot flame heats a component called the thermocouple—a metal rod positioned directly in the flame. When the thermocouple gets hot enough, it generates a small electrical current that signals the gas valve to stay open. If the pilot goes out, the thermocouple cools down, the electrical signal stops, and the gas valve closes. That's your safety mechanism: no flame, no gas flow.
Newer furnaces—Carrier, Lennox, Trane, Bryant models built after roughly 2005—use electronic ignition systems instead. These systems only ignite gas when the thermostat calls for heat, eliminating the constant pilot flame. They're more efficient (a standing pilot burns about 600-900 BTUs per hour, 24/7) and more reliable, but they cost more upfront.
If you have a furnace with a standing pilot and it keeps going out, the safety system is doing its job. Something is preventing the pilot from staying lit or preventing the thermocouple from sensing the flame properly.
The 5 Most Common Reasons Your Pilot Light Won't Stay Lit
1. Failed Thermocouple (The #1 Culprit)
The thermocouple is a wear item. After years of constant heating and cooling cycles, the metal degrades and stops generating enough voltage to keep the gas valve open. You'll light the pilot, it looks perfect, you release the button—and it goes out within seconds.
Thermocouples cost $20-$50 for the part. A service call to replace one typically runs $150-$250 in Southeast Michigan, depending on the contractor and furnace accessibility. It's a 20-minute job for a trained tech. If your furnace is 15+ years old and you've never replaced the thermocouple, this is almost certainly your problem.
2. Dirty Flame Sensor or Pilot Orifice
Dust, rust, and carbon buildup can clog the tiny pilot orifice (the opening where gas flows to create the pilot flame). When the orifice is partially blocked, the flame becomes weak, small, or yellow instead of blue. A weak flame doesn't heat the thermocouple properly, so the safety system shuts off the gas.
Similarly, if the flame sensor itself is coated in soot or corrosion, it can't detect the flame accurately. This is especially common in furnaces that sit in dusty basement utility rooms or near laundry areas where lint accumulates.
Cleaning the pilot assembly and flame sensor is part of a standard furnace tune-up. If you're enrolled in a preventive maintenance plan like the Next Care Plan, this gets done every fall before heating season—which is exactly why our members rarely deal with pilot light failures mid-winter.
3. Draft Issues (Basement Furnace Rooms and Backdrafting)
Michigan basements are notorious for creating draft problems. If your furnace is in an older home with a natural-draft chimney or vent, negative air pressure can literally blow out the pilot flame. This happens when:
Bathroom or kitchen exhaust fans create negative pressure in the house
The furnace room door is closed and there's insufficient combustion air
A cracked heat exchanger or poorly sealed vent allows backdrafting
High winds outside create downdrafts through the chimney
If your pilot goes out primarily on windy days or when certain exhaust fans are running, you have a draft problem. This isn't something you fix with a new thermocouple—it requires evaluating combustion air supply, venting, and potentially upgrading to a sealed-combustion furnace.
Safety Note: Draft issues can cause carbon monoxide to spill into your living space instead of venting safely outside. If you smell exhaust fumes near your furnace or experience headaches, dizziness, or nausea when the furnace runs, turn it off immediately and call for service. Install CO detectors on every floor.
4. Gas Pressure Problems
Natural gas is delivered to your home at a specific pressure, and your furnace's gas valve regulates it down to the precise level needed for the pilot and burners. If the incoming gas pressure is too low—due to a problem with the utility company's supply or a partially closed manual shutoff valve—the pilot flame will be weak and unstable.
This is rare, but we see it occasionally in areas with older gas infrastructure or after utility work in the neighborhood. A tech can measure gas pressure at the furnace inlet with a manometer. Residential natural gas should arrive at 7-10 inches of water column (about 0.25-0.36 psi). If it's significantly lower, the gas company needs to investigate.
5. Faulty Gas Valve
The gas valve itself can fail. Internal components wear out, seals degrade, or the electromagnetic coil that controls gas flow stops working correctly. If the valve isn't opening fully or is cycling erratically, the pilot won't stay lit even if the thermocouple is functioning.
Gas valve replacement is more expensive—typically $300-$600 depending on the furnace model and valve type. Carrier, Lennox, and Trane furnaces use different valve designs, and older models sometimes require hard-to-find parts. If your furnace is 20+ years old and needs a gas valve, that's often the point where replacement makes more financial sense than repair.
How to Safely Relight Your Pilot (When It's Appropriate)
If your pilot has gone out once and you don't smell gas, you can try relighting it yourself. Most furnaces have instructions printed on a label near the gas valve. Here's the general process:
Turn the gas valve to OFF. Wait at least 5 minutes to allow any accumulated gas to dissipate. This is critical—skipping this step risks a flashback or small explosion when you ignite the pilot.
Check for gas smell. If you smell natural gas (rotten egg odor) or propane, do not attempt to relight. Leave the house immediately, call your gas company from outside, and do not use any electronics or light switches inside.
Turn the valve to PILOT. You may need to press down on the valve while turning it.
Light the pilot. While holding down the pilot button or reset button, use a long lighter or match to ignite the pilot. You should see a small blue flame at the pilot assembly.
Hold for 30-60 seconds. Keep holding the button down after the flame ignites. This gives the thermocouple time to heat up and generate the electrical signal that tells the gas valve it's safe to keep gas flowing.
Release and test. Slowly release the pilot button. The flame should stay lit. If it goes out immediately, the thermocouple is likely bad.
Turn to ON. Once the pilot stays lit, turn the gas valve to the ON position. Set your thermostat to call for heat and verify the burners ignite properly.
If the pilot stays lit for a few hours or a day and then goes out again, stop trying to fix it yourself. You have an underlying problem that needs professional diagnosis.
When DIY Ends and Professional Repair Begins
Call a licensed HVAC contractor if:
The pilot won't stay lit after you release the button (thermocouple failure)
You've relit the pilot multiple times and it keeps going out
The pilot flame is yellow, orange, or flickering instead of steady blue
You smell gas at any point in the process
The furnace is making unusual noises—rumbling, banging, or whistling
You see rust, corrosion, or soot around the burner area
Your carbon monoxide detector goes off
A yellow or orange pilot flame indicates incomplete combustion, which produces carbon monoxide. A properly adjusted pilot should be a crisp blue cone with a small yellow tip. If yours looks different, don't run the furnace—call for service.
The cost to repair a pilot light issue depends on the diagnosis. Here's what we typically see in Macomb, Oakland, and St. Clair counties:
Thermocouple replacement: $150-$250
Pilot assembly cleaning: $100-$175 (often included in a tune-up)
Gas valve replacement: $300-$600
Draft/venting correction: $200-$800 depending on scope
Full furnace replacement: $3,500-$7,500 for a mid-efficiency model in a typical Michigan home
If your furnace is 15-20 years old and you're facing a $400+ repair, it's worth getting a replacement quote. Modern furnaces are significantly more efficient (95%+ AFUE vs. 80% for older models), more reliable, and come with warranties. A licensed and insured HVAC contractor can run a proper heat load calculation and give you honest options—not a high-pressure sales pitch.
Why Michigan Basements Make Pilot Light Problems Worse
If you live in an older home in Clinton Township, Warren, or Grosse Pointe Farms, your furnace is probably in a basement utility room built decades before modern building codes addressed combustion air requirements. Here's why that matters:
Combustion air supply: Gas furnaces need air to burn fuel safely. Older furnaces pull combustion air from the room they're in—which is fine if the room is large and drafty. But if your furnace is in a small, sealed utility room with a tight-fitting door, it can run out of oxygen. The pilot flame becomes starved for air and goes out.
Modern code (NFPA 54, Michigan Mechanical Code) requires either two permanent openings to the outdoors or a direct combustion air duct to the furnace. If your furnace room doesn't have this, you may need to add ventilation or upgrade to a sealed-combustion furnace that draws air from outside through a PVC pipe.
Negative pressure from exhaust fans: When you run a bathroom exhaust fan, kitchen range hood, or whole-house ventilation system, it creates negative pressure inside the home. Air has to come from somewhere to replace what's being exhausted. If your furnace vent isn't sealed properly, that negative pressure can pull combustion gases back down the chimney or vent pipe—a condition called backdrafting. This can blow out the pilot or, worse, pull carbon monoxide into your living space.
We've seen this dozens of times in homes around Lake Orion and Rochester Hills: the pilot stays lit all day, then the homeowner runs the bathroom fan before bed and the pilot goes out overnight. That's a clear sign of a draft/pressure imbalance that needs professional correction.
Cold basement temperatures: Michigan basements stay cold in winter. If your furnace vent pipe runs through an uninsulated rim joist area or along an exterior wall, condensation can form inside the vent. In extreme cold, that condensation can freeze and partially block the vent, creating backdrafting. This is especially common with older B-vent (natural draft) systems.
Should You Upgrade to Electronic Ignition?
If you're facing a repair bill on a furnace that's 15+ years old, it's worth considering an upgrade to a modern electronic ignition system. Here's the practical reality:
Efficiency gains: A standing pilot burns 600-900 BTUs per hour, 24/7, year-round. That's roughly 5-8 therms per month of wasted gas just keeping the pilot lit—about $6-$12 per month at current Michigan gas rates, or $70-$140 per year. Over a 15-year furnace lifespan, that's $1,000-$2,000 in pilot fuel alone.
Electronic ignition furnaces (hot surface ignition or intermittent pilot) only use gas when heating. They also tend to be higher-efficiency models overall—95%+ AFUE compared to 80% for most standing-pilot furnaces. On a typical 1,800-square-foot Michigan home, upgrading from an 80% to a 95% furnace can save $300-$500 per year in heating costs.
Reliability benefits: No pilot means no thermocouple failures, no pilot outages, no relighting. Modern furnaces use solid-state controls and hot surface igniters that last 10-15 years with minimal maintenance. You'll still need annual tune-ups (flame sensor cleaning, blower maintenance, heat exchanger inspection), but the ignition system itself is essentially maintenance-free.
Cost comparison: A mid-efficiency (80% AFUE) furnace replacement in Southeast Michigan typically runs $3,500-$5,000 installed. A high-efficiency (95%+ AFUE) two-stage modulating furnace runs $5,500-$7,500. That's a $2,000-$2,500 premium for the better system, but you'll recoup most of that in energy savings over 8-10 years—and you'll have better comfort, quieter operation, and longer equipment life.
Brands we install regularly—Carrier Infinity series, Lennox SLP98V, Trane XV95, Bryant Evolution—all use electronic ignition and come with 10-year parts warranties. If you're in a home you plan to stay in for 10+ years, the math strongly favors upgrading now rather than repairing an aging furnace repeatedly.
Our NATE-certified HVAC technicians can walk you through the options without pressure. We've been doing this since 1991 under Premier Builder Inc., and we don't do commission-based sales. You'll get honest diagnostics, real cost comparisons, and a recommendation based on your home and budget—not our sales targets.
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NEXT Heating & Cooling has been keeping Michigan homes comfortable for over 35 years. Get honest diagnostics and fair pricing from NATE-certified technicians who show up on time.
Frequently Asked Questions
How much does it cost to replace a thermocouple in Michigan?+
Thermocouple replacement typically costs $150-$250 for a service call in Southeast Michigan, including the part and labor. The thermocouple itself is only $20-$50, but you're paying for the technician's diagnostic time, travel, and expertise. If you're already having an annual furnace tune-up, the tech may replace it as part of the service for less.
Can I replace a thermocouple myself?+
Technically, yes—it's a simple mechanical connection. But you're working with gas, and if you cross-thread the fitting or don't tighten it properly, you risk a gas leak. Most homeowners don't have the right wrenches or the experience to do it safely. Unless you're very comfortable with gas appliance work, call a licensed tech. The cost difference between DIY and professional isn't worth the risk.
Why does my pilot light go out only on windy days?+
Wind creates downdrafts in your furnace vent or chimney, which can blow out the pilot flame. This is a sign of inadequate draft protection or a venting problem. Older natural-draft furnaces are especially vulnerable. Solutions include installing a draft hood, upgrading to a sealed-combustion furnace, or correcting the vent termination height and location. A tech needs to evaluate your specific venting setup.
Is it dangerous if my furnace pilot light keeps going out?+
The pilot going out itself isn't dangerous—the safety system is working correctly by shutting off gas flow when there's no flame. But the underlying cause can be dangerous. If you have a draft problem, cracked heat exchanger, or venting issue, you could be at risk for carbon monoxide exposure. Never ignore a pilot that goes out repeatedly. Get it diagnosed by a licensed HVAC contractor.
How long should a thermocouple last?+
A thermocouple typically lasts 10-15 years under normal use. Factors that shorten its life include pilot flame issues (too weak or too strong), corrosion from basement humidity, and physical damage from maintenance work. If your furnace is 15+ years old and you've never replaced the thermocouple, it's likely near the end of its service life.
Should I turn off the gas to my furnace in summer?+
If you have a standing pilot, turning off the gas in summer saves about $70-$140 per year in pilot fuel costs. But you'll need to relight it in fall, and if the thermocouple has degraded over the summer, you may have trouble getting it to stay lit. Most homeowners leave it running for convenience. If you do turn it off, have a professional relight it and inspect the furnace before heating season—don't wait until the first cold night in November.
What's the difference between a thermocouple and a flame sensor?+
A thermocouple is used in older furnaces with standing pilots—it's a metal rod that generates voltage when heated by the pilot flame. A flame sensor is used in modern electronic ignition furnaces—it's a metal probe that detects the presence of flame using electrical current. Both serve the same purpose (proving flame presence for safety), but they work differently. If your furnace has a pilot light, it uses a thermocouple. If it has electronic ignition, it uses a flame sensor.