Gas Furnace Pilot Light Keeps Going Out? Here's Why
You walk down to your basement furnace room in Sterling Heights on a January morning, thermostat set to 68°, but the house feels like 62°. You check the furnace and find the pilot light out — again. You relight it, and it stays on for a day or two, then goes out. Maybe it happens every week. Maybe it's happened three times this month.
A gas furnace pilot light that keeps going out isn't just annoying — it's a safety issue and a sign something in your heating system needs attention. After 35 years of furnace installation and repair across Southeast Michigan, we've diagnosed this exact problem hundreds of times in homes from Macomb Township to Royal Oak.
Here's what's actually happening, why your pilot light keeps going out, and when you need to call a licensed HVAC contractor instead of relighting it yourself.
What the Pilot Light Actually Does (And Why It Matters)
If your furnace was installed before the mid-2000s, it likely uses a standing pilot ignition system. This is a small, continuous flame that burns 24/7 during the heating season. When your thermostat calls for heat, the gas valve opens, and the pilot light ignites the main burners.
The pilot flame does more than just light the burners — it heats a safety device called a thermocouple (or flame sensor, depending on your furnace model). The thermocouple is a metal rod positioned directly in the pilot flame. When heated, it generates a small electrical current that tells the gas valve it's safe to stay open.
Here's the critical safety mechanism: if the pilot flame goes out, the thermocouple cools down within seconds. Once it cools, it stops generating current, and the gas valve automatically shuts off. This prevents unburned gas from filling your furnace cabinet or basement — a serious explosion and carbon monoxide risk.
So when your pilot light keeps going out, the furnace is doing exactly what it's designed to do: shutting down to protect you. But the underlying cause still needs to be fixed.
6 Reasons Your Gas Furnace Pilot Light Keeps Going Out
We see the same patterns repeat across older furnaces in Michigan homes — especially Carrier, Lennox, Rheem, and Bryant models from the 1990s and early 2000s. Here are the six most common causes, ranked by how often we find them during service calls.
1. Dirty or Faulty Thermocouple
This is the number one cause. The thermocouple sits in the pilot flame constantly. Over years of use, it accumulates carbon deposits, dust, and oxidation. A dirty thermocouple can't sense the flame properly, so it signals the gas valve to shut off — even when the pilot is lit.
In other cases, the thermocouple simply wears out. The metal degrades, the wiring connection loosens, or internal components fail. A thermocouple typically costs $20-$50 for the part and takes about 30 minutes to replace. It's one of the most straightforward furnace repairs we do.
What you'll notice: The pilot lights easily but goes out after 10-30 seconds, or it stays lit for a few hours then shuts off randomly.
2. Draft or Airflow Issues
Michigan basements are drafty. We've seen pilot lights blown out by air leaking through foundation cracks, improperly sealed ductwork, or even a basement door left open during a windstorm. If your furnace is installed near a window, exterior door, or fresh air intake, a strong gust can extinguish the pilot.
We also see this in furnaces installed in utility closets or tight spaces where there's not enough combustion air. Gas furnaces need oxygen to burn properly. If the room is too sealed or the furnace is starved for air, the pilot flame can become unstable and go out.
What you'll notice: The pilot goes out during windy days, after opening a basement door, or when the furnace first fires up and creates negative pressure.
3. Dirty Pilot Orifice
The pilot orifice is a tiny brass fitting that controls the flow of gas to the pilot flame. It's about the size of a pencil eraser, with a hole smaller than a pin. Over time, dust, rust, and debris can partially clog this orifice, reducing gas flow and weakening the pilot flame.
A weak pilot flame won't generate enough heat to keep the thermocouple activated. The flame might look smaller than usual, flicker, or burn yellow instead of blue. Cleaning the orifice usually solves the problem — it's a simple procedure, but it requires removing the pilot assembly and using compressed air or a fine wire to clear the blockage.
What you'll notice: The pilot flame is small, yellow, or flickers. It may go out when the main burners ignite and create air movement.
4. Gas Supply Problems
If the gas pressure to your furnace is too low, the pilot won't stay lit. This can happen if:
- The gas valve supplying the furnace is partially closed
- There's a pressure regulator issue at the meter
- Your gas company is experiencing supply problems (rare but happens during extreme cold)
- There's a leak in the gas line reducing pressure
We saw this frequently during the polar vortex events in 2014 and 2019, when natural gas demand spiked and some areas experienced temporary pressure drops. If you smell gas or suspect a leak, leave your home immediately and call your gas company — never try to diagnose this yourself.
What you'll notice: The pilot is difficult to light, won't stay lit at all, or goes out when other gas appliances (water heater, stove) turn on.
5. Faulty Gas Valve
The gas valve is the brain of your furnace's fuel delivery system. It controls gas flow to both the pilot and the main burners. If the valve's internal components fail — particularly the electromagnetic coil that holds the valve open — the pilot will go out repeatedly.
Gas valve failures are less common than thermocouple issues, but they do happen, especially in furnaces 15+ years old. Brands like Honeywell and White-Rodgers make the valves used in most Carrier, Lennox, and Rheem furnaces. A replacement gas valve typically costs $300-$600 installed, depending on the model.
What you'll notice: You've already replaced the thermocouple, cleaned the orifice, and the pilot still won't stay lit. The gas valve may click or hum but fail to maintain gas flow.
6. Venting and Exhaust Problems
Your furnace needs to exhaust combustion gases safely through a vent pipe or chimney. If the vent is blocked — by a bird's nest, ice buildup, or debris — exhaust gases can back up into the furnace cabinet. This creates a dangerous situation where carbon monoxide can't escape, and the pilot flame becomes unstable.
We see vent blockages most often in older homes in Clinton Township and Warren with shared chimneys (where the furnace and water heater vent into the same flue). If the chimney isn't properly lined or if the draft is poor, the pilot can be affected.
Modern furnaces have safety switches that detect this and shut down the system. Older furnaces may not, which is why a pilot that keeps going out should never be ignored.
What you'll notice: You smell exhaust fumes near the furnace, the pilot goes out shortly after the main burners fire, or you see soot around the burner compartment.
When to Call a Technician (And What We Check)
You can safely relight your pilot light once or twice if it goes out. But if it keeps happening, don't keep relighting it — call a professional. Here's when you need a reliable HVAC contractor in Metro Detroit:
Safety red flags that require immediate professional service:
- You smell gas (rotten egg odor) near the furnace or in your home
- The pilot flame is yellow or orange instead of blue
- You see soot or black residue around the burners or vent
- The furnace cabinet feels excessively hot
- Your carbon monoxide detector is alarming
- The pilot goes out immediately after relighting, every time
When you call NEXT Heating & Cooling for a pilot light issue, here's what our NATE-certified technicians check during the diagnostic visit:
- Thermocouple condition and positioning: We test the millivolt output to ensure it's generating proper current (usually 25-30 millivolts when heated). We also check that it's positioned correctly in the flame — even a few millimeters off can cause problems.
- Pilot orifice and flame quality: We inspect the pilot flame color (should be blue with a small yellow tip), size, and stability. We clean the orifice if needed.
- Gas pressure: We measure inlet and manifold pressure to ensure your furnace is getting the right amount of gas (typically 3.5" water column for natural gas).
- Venting and combustion air: We inspect the vent pipe for blockages, check draft, and ensure your furnace has adequate combustion air.
- Gas valve operation: We test the valve's electrical components and listen for proper operation when the thermostat calls for heat.
- Overall furnace condition: We look at the heat exchanger, burners, blower, and safety controls to identify any other issues that could affect pilot light operation or safety.
Most pilot light repairs cost between $150-$400, depending on the cause. A thermocouple replacement is on the lower end. A gas valve replacement is on the higher end. If your furnace is 20+ years old and needs a major repair, we'll have an honest conversation about whether repair or replacement makes more sense — we've covered this in detail in our guide to furnace replacement costs in Michigan.
How to Relight Your Pilot Light Safely
If your pilot light has gone out and you don't smell gas, you can try relighting it yourself. Every furnace is slightly different, so check the instructions printed on your furnace cabinet first. Here's the general process for most standing pilot systems:
- Turn the gas valve to OFF. Locate the gas control valve on your furnace (usually a red or black knob with settings for OFF, PILOT, and ON). Turn it to OFF and wait at least 5 minutes. This allows any accumulated gas to dissipate.
- Locate the pilot light assembly. You'll usually find it behind a small access panel near the bottom of the furnace. You should see the pilot tube (a small copper or steel tube) and the thermocouple (a thicker rod positioned next to the pilot).
- Turn the valve to PILOT. Turn the gas control valve to the PILOT position. Press and hold the reset button or pilot button (this manually opens the gas valve).
- Light the pilot. While holding the button down, use a long lighter or match to ignite the pilot flame. You should see a small blue flame at the end of the pilot tube. Keep holding the button for 30-60 seconds after the flame lights — this gives the thermocouple time to heat up.
- Release and test. Slowly release the button. The pilot flame should stay lit. If it goes out immediately, wait 5 minutes and try again. If it goes out after you release the button, the thermocouple likely needs cleaning or replacement.
- Turn to ON. Once the pilot stays lit, turn the gas valve to the ON position. Replace the access panel and set your thermostat to call for heat. The main burners should ignite.
When NOT to attempt relighting:
- If you smell gas — leave immediately and call your gas company
- If the pilot has gone out more than twice in a week
- If you're uncomfortable working with gas appliances
- If the furnace cabinet is hot or you see visible damage
Modern furnaces with electronic ignition (installed after 2005 or so) don't have standing pilots. If you have a newer furnace and it's not starting, the issue is different — usually an igniter, flame sensor, or control board problem. You'll need professional diagnosis for those systems.
Preventing Future Pilot Light Problems
Most pilot light issues are preventable with regular maintenance. Here's what actually works based on what we see in the field:
Annual Professional Maintenance
A yearly furnace tune-up catches thermocouple wear, pilot orifice buildup, and gas pressure issues before they cause breakdowns. Our Next Care Plan includes two annual visits — a fall furnace tune-up and a spring AC tune-up — for just $5/month. During the fall visit, we clean the pilot assembly, test the thermocouple, inspect the gas valve, and verify proper combustion and venting.
We've found that furnaces on a maintenance plan have 60-70% fewer mid-winter breakdowns than furnaces that only get serviced when something breaks. The thermocouple alone can last 3-5 years longer when it's cleaned annually instead of left to accumulate carbon deposits.
Change Your Air Filter Regularly
A clogged air filter restricts airflow, which can create negative pressure in your furnace cabinet. This affects combustion air and can destabilize the pilot flame. We recommend checking your filter monthly during heating season and replacing it every 1-3 months depending on the type (fiberglass filters monthly, pleated filters every 2-3 months, high-efficiency filters per manufacturer instructions).
Seal Drafts and Ensure Combustion Air
If your furnace is in a basement or utility room, make sure there's adequate ventilation. Older homes in Troy and Bloomfield Hills often have furnaces in sealed mechanical rooms with no fresh air supply. The Michigan Mechanical Code requires combustion air openings for gas furnaces — typically two openings (high and low) to the outdoors or to a well-ventilated space.
At the same time, seal obvious drafts that could blow out the pilot. We've seen pilots extinguished by air leaking through dryer vents, basement windows with broken seals, and foundation cracks.
Consider Upgrading to Electronic Ignition
If your furnace is 15-20 years old and you're dealing with repeated pilot light problems, it might be time to upgrade. Modern high-efficiency furnaces (95%+ AFUE) use electronic ignition — either hot surface igniters or intermittent pilot systems. These eliminate the standing pilot entirely, which saves gas, improves efficiency, and removes the most common failure point.
A new furnace is an investment — typically $3,500-$7,000 installed for most Michigan homes, depending on size and efficiency — but if you're facing a $500 gas valve replacement on a 20-year-old furnace, replacement often makes more financial sense. We break down the real numbers in our furnace replacement cost guide.
Pilot Light Keeps Going Out? We'll Find the Cause
NEXT Heating & Cooling has been diagnosing and repairing furnaces across Southeast Michigan for over 35 years. Our NATE-certified technicians will identify exactly why your pilot won't stay lit and give you honest options — repair or replace, no pressure.
Schedule Your Service CallFrequently Asked Questions
The pilot light going out itself isn't dangerous — your furnace has a safety mechanism (the thermocouple) that shuts off gas flow when the pilot goes out. However, the underlying cause could be dangerous. If you smell gas, see yellow flames, or notice soot buildup, those are signs of incomplete combustion or venting problems that can produce carbon monoxide. Never ignore a pilot light that repeatedly goes out — have it professionally diagnosed.
Most pilot light repairs cost $150-$400 in Southeast Michigan. A thermocouple replacement (the most common fix) typically runs $150-$250 including labor. Cleaning a dirty pilot orifice is often part of a standard service call ($100-$150). A gas valve replacement is more expensive — usually $300-$600 depending on the furnace model. At NEXT Heating & Cooling, we diagnose the issue first and give you an exact price before starting any work.
A properly functioning standing pilot light should stay lit continuously throughout the entire heating season — from October through April in Michigan. You should never have to relight it more than once or twice a season (and ideally not at all). If your pilot is going out weekly, daily, or even multiple times per day, there's a mechanical problem that needs professional repair.
You can safely relight your pilot once or twice if it goes out unexpectedly. But if it keeps going out, don't keep relighting it — call a technician. Repeatedly relighting a failing pilot can be dangerous if there's a gas leak, venting problem, or carbon monoxide issue. Plus, you're just delaying an inevitable repair. The underlying problem won't fix itself, and it may get worse and more expensive the longer you wait.
A healthy pilot light should be mostly blue with a small yellow tip. The blue color indicates complete combustion — the gas is burning efficiently with enough oxygen. If your pilot flame is mostly yellow or orange, that's a sign of incomplete combustion, which can be caused by a dirty orifice, poor air mixture, or venting problems. A yellow flame produces soot and carbon monoxide. If you see this, turn off your furnace and call for service immediately.
If your pilot goes out the moment the main burners ignite, it's usually caused by airflow disruption. When the burners fire, they create air movement inside the furnace cabinet. If the pilot flame is weak (due to a dirty orifice or low gas pressure) or if there's a draft in the furnace room, that air movement can blow out the pilot. This can also indicate a venting problem where exhaust gases aren't leaving the furnace properly and are creating turbulence.
It's generally safe to turn off your pilot light during Michigan's warmer months (May-September) if you want to save a small amount on your gas bill. A standing pilot burns about $5-$10 worth of gas per month. However, if you turn it off, you'll need to relight it in the fall before heating season. Some homeowners prefer to leave it on year-round to avoid the hassle. If you do turn it off, follow your furnace's shutdown instructions carefully, and consider having a professional relight it in the fall as part of a pre-season tune-up.