January 13, 2026
Few furnace problems frustrate homeowners more than a pilot light that repeatedly goes out. You light it, the flame appears steady, you walk away confident the problem is solved, only to return hours or days later to find it extinguished again. This cycle of relighting and disappointment not only leaves your home cold but raises legitimate safety concerns about your gas furnace operation.
During our 25+ years of service, we've responded to hundreds of pilot light calls. While the symptom remains consistent, the pilot flame won't stay lit; the underlying causes vary significantly in both frequency and seriousness. Some require simple 5-minute fixes you can handle yourself, while others demand immediate professional attention for safety reasons.
Understanding why pilot lights go out, identifying the specific causes, and knowing when DIY fixes are appropriate and when professional help is essential allows you to respond quickly and appropriately. This guide ranks the six most common causes by frequency based on our field experience, explains the diagnostic steps for each, and provides realistic cost expectations so you know what to expect.
6 Causes of Pilot Light That Won't Stay Lit (Ranked by Frequency)
Cause #1: Faulty or Dirty Thermocouple (40% of Cases)
What's Happening: The thermocouple is a small copper sensor that sits in the pilot flame. When it heats up, it generates a low electrical signal that keeps the gas valve open. If it's dirty, out of position, or failing, it can't produce a strong enough signal, so the gas valve closes and the pilot shuts off.
How to Identify This Issue
Pilot lights but goes out within seconds or minutes after releasing the control knob
Pilot flame looks steady and blue
Pilot consistently goes out after the same time interval
The thermocouple looks dirty, corroded, or bent away from the flame
The pilot goes out immediately after releasing the pilot button or control knob
The furnace is several years old (thermocouples weaken over time)
Why It Happens: Over time, thermocouples accumulate carbon buildup, preventing proper heating. They can also get bumped out of alignment during maintenance or filter changes. Dust and debris in the furnace area can speed up fouling. Eventually, the metal junction inside the thermocouple wears down, reducing the electrical output needed to keep the gas valve open.
The Fix - Professional: If cleaning doesn't help, the thermocouple likely needs to be replaced. This is a quick, routine repair for an HVAC technician.
Prevention: Annual furnace maintenance typically includes inspecting and cleaning the thermocouple. Regular service helps prevent pilot-out issues and extends thermocouple life.
Cause #2: Draft or Airflow Problems (25% of Cases)
What's Happening: Drafts can blow out the pilot flame the same way a breeze extinguishes a candle. The pilot is small and sensitive to air movement from open doors, nearby vents, return-air pulls, or ventilation issues. Even mild airflow you may not notice can disrupt combustion and extinguish the flame.
How to Identify This Issue
Pilot goes out at unpredictable times rather than after a consistent interval
Outages coincide with doors opening, HVAC operation, or windy conditions
Furnace is in a garage, basement, or utility room near an exterior door
Pilot flame visibly flickers or wavers when burning
Issue started after home updates, door changes, or ventilation modifications
More common during windy weather or when windows are open
Why It Happens: A stable air environment is critical for the pilot flame. Drafts can develop from loose furnace panels, gaps around furnace-room doors, poorly sealed walls, blocked or improperly installed flue vents, nearby return-air suction, cross-drafts from open windows or doors, or exhaust fans that alter airflow. Shifts in the home structure over time can also create new gaps or airflow paths that didn't exist when the system was installed.
The Fix - Professional: If drafts persist, a technician can evaluate the flue system, repair venting issues, add a draft hood, modify duct placement, or recommend ventilation improvements. More complex airflow problems may require a full inspection of the surrounding ductwork or vent paths.
Prevention: Keep the furnace area sealed and free from strong airflow. Limit door and window openings near the furnace during operation, and ensure the furnace room maintains consistent, draft-free conditions.
Cause #3: Low Gas Pressure or Gas Supply Issues (15% of Cases)
What's Happening: The pilot flame needs steady gas pressure to burn reliably. When pressure drops, the flame becomes weak and unstable, eventually extinguishing. Low pressure can stem from issues with the home's gas supply, the main gas valve, the gas regulator, or restrictions in the gas line.
How to Identify This Cause
The pilot flame looks weak, yellow, or flickering instead of strong and blue
Flame appears smaller than normal
Other gas appliances (water heater, stove, etc.) show reduced performance
The issue began after utility work on nearby gas lines
The main gas valve may be only partially open
Pilot lights easily but gradually weakens before going out
Why This Happens: Gas pressure can drop for several reasons. A main gas valve that isn't fully open limits flow. A failing gas regulator can't maintain proper pressure. Kinked, damaged, or obstructed gas lines restrict supply. Utility-side problems can temporarily lower neighborhood pressure. In some situations, multiple gas appliances running simultaneously can temporarily reduce available pressure. Sediment or debris inside the gas line can also cause a partial blockage.
The Fix - Professional Required: Diagnosing gas pressure requires specialized testing. Technicians use manometers to measure pressure throughout the system and pinpoint whether the issue lies with the utility supply, home gas lines, the regulator, or the furnace connections. Gas-related repairs must be handled by licensed professionals for safety and compliance.
Prevention: Keep gas valves fully open, have gas pressure tested during routine maintenance, and address any gas appliance performance changes early to prevent larger issues.
Cause #4: Clogged or Dirty Pilot Orifice (10% of Cases)
What's Happening: The pilot orifice is a very small opening that allows gas to flow and form the pilot flame. Over time, this opening can become partially blocked by dust, dirt, spider webs, or carbon buildup. Even a slight obstruction weakens the flame, distorts its shape, and prevents it from properly heating the thermocouple, eventually causing the pilot to go out.
How to Identify This Cause
Pilot flame looks irregular; split, angled, or uneven
Flame appears weak despite normal gas pressure
Visible dust, debris, or spider webs around the pilot assembly
Pilot performance declined gradually over weeks or months
Issue started after the furnace sat unused for a long period
Furnace is in a dusty area such as a garage, basement, or utility room
Why This Happens: Pilot orifices are extremely small, making them sensitive to minor contamination. When the furnace sits idle for long periods, dust settles in the assembly, and insects, especially spiders, can block the orifice with webs. Combustion byproducts also create carbon deposits over time. Homes with dusty mechanical rooms, basements, or garages tend to see orifice fouling more quickly.
The Fix - Professional Option: A technician can clean the orifice using proper tools or replace the pilot assembly if the orifice is damaged or cleaning doesn't resolve the issue.
Prevention: Keep the furnace area as clean as possible to limit dust buildup. Include pilot assembly cleaning during routine maintenance. Some homeowners cover the assembly during the off-season; do so only under a technician's guidance to ensure safe airflow and proper ventilation.
Cause #5: Pilot Flame Adjustment Needed (7% of Cases)
What's Happening: Pilot flames need to meet specific height and burn characteristics, typically a steady blue flame around 1.5 to 2 inches tall. If the flame is set too low, it won't heat the thermocouple enough to keep the gas valve open. If it's too high, it can create soot and burn inefficiently. A small adjustment screw on the gas valve controls flame size, and this setting can drift over time or get bumped during maintenance.
How to Identify This Cause
Pilot flame is noticeably smaller than the recommended height
Flame barely reaches the thermocouple tip
Pilot goes out more often during cold weather when the thermocouple needs more heat
Issue started after recent service or maintenance
Other causes (drafts, gas pressure, thermocouple issues) have been ruled out
Changing the pilot adjustment screw affects how long the pilot stays lit
Why This Happens: Pilot adjustment settings can shift from vibration during furnace operation, accidental bumps during filter changes, aging or wear in the gas valve mechanism, or temperature-related expansion and contraction. In some cases, a previous homeowner may have adjusted the pilot without restoring it to proper settings.
The Fix - Professional Option: A technician can adjust the pilot flame to manufacturer specifications using the furnace's data plate and their instruments, ensuring optimal flame height and safe operation.
Prevention: Have the pilot flame checked during routine maintenance. Avoid touching adjustment screws during filter changes or cleaning. If you ever make adjustments yourself, note the original position in case you need to restore it.
Cause #6: Faulty Gas Valve or Control System (3% of Cases)
What's Happening: The gas control valve manages all gas flow to your furnace, including the pilot supply and safety shutoff functions. Inside are electrical components, regulators, and an electromagnet that responds to the thermocouple's signal. When these internal parts fail—especially the electromagnet—the valve shuts off gas to the pilot even when it should remain open.
How to Identify This Cause
Pilot goes out immediately when you release the pilot or reset button
Failure is consistent every time, within seconds
Replacing the thermocouple didn't fix the issue
Gas valve makes clicking sounds or feels unusually warm
Pilot stays lit only while the button is held down
Furnace is older with its original gas valve
Other likely causes have already been ruled out
Why This Happens: Gas valves contain coils, springs, diaphragms, and safety mechanisms that degrade over time. The electromagnet can weaken, internal parts can become overly sensitive, and electrical contacts can corrode. Sediment may interfere with internal movement. Repeated expansion and contraction from seasonal temperature changes also stress valve components. Most valves have a long service life, but age, environmental conditions, and lack of maintenance can accelerate failure.
Prevention: Regular professional maintenance helps spot valve issues early. Technicians can test valve function, check electrical signals, and confirm proper operation. Addressing pilot problems early, rather than repeatedly relighting the furnace, reduces strain on gas valve components.
When to Call Professional Help Immediately
Certain situations with pilot lights require immediate professional attention for safety reasons. Contact licensed HVAC technicians right away if you experience:
- Strong smell of natural gas around furnace (rotten egg/sulfur odor)
- A hissing sound indicating a gas leak
- Carbon monoxide detector alarms
- Pilot repeatedly goes out multiple times per day
- Difficulty breathing, headaches, dizziness, or nausea in household members
- The pilot won't light at all despite following the proper lighting procedure
- Yellow or orange pilot flame (should be blue)
- Soot or black marks around the pilot assembly or burners
- Visible damage to gas lines, connections, or furnace components
- Water accumulation around the furnace
Gas furnaces are generally safe when properly maintained, but malfunctions can create serious hazards. When in doubt, err on the side of caution and call for professional inspection.
Safety Considerations and Carbon Monoxide Risks
A pilot light that repeatedly goes out isn't just an inconvenience; it can indicate conditions that pose carbon monoxide risks. Here's what you need to know:
Carbon Monoxide and Pilot Lights
Pilot lights that go out don't directly produce carbon monoxide. However, the underlying causes (dirty burners, improper combustion, ventilation problems, or gas valve issues) can create conditions where the main burner produces dangerous carbon monoxide when it does run. This is why carbon monoxide detectors are essential for any home with gas appliances.
Install and Maintain Carbon Monoxide Detectors
Place carbon monoxide detectors on every level of your home, especially near sleeping areas and the furnace room. Test detectors monthly and replace batteries twice yearly (an easy way to remember: change them when you change clocks for daylight saving time). Replace entire detector units every 5-7 years per manufacturer recommendations.
Recognize Carbon Monoxide Symptoms
Carbon monoxide poisoning symptoms include headaches, dizziness, weakness, nausea, vomiting, chest pain, and confusion. Symptoms that worsen when you're home and improve when you leave could indicate carbon monoxide exposure. If you suspect carbon monoxide poisoning, evacuate immediately and call 911 from outside the home.
Conclusion
A furnace pilot light that repeatedly goes out frustrates homeowners and leaves homes uncomfortably cold, but understanding the six most common causes, ranked from most to least frequent, allows you to respond appropriately.
At MR. HVAC, we've diagnosed and repaired thousands of pilot light problems in Local communities. Our technicians carry thermocouples, pilot assemblies, and other common parts on their service vehicles, allowing us to complete most repairs during the initial visit. We understand that furnace problems create urgency, especially during North Georgia's coldest winter nights.
Don't spend another cold night constantly relighting your furnace pilot. Contact MR. HVAC today for professional pilot light diagnosis and repair. We offer same-day emergency service and can typically respond within hours of your call. Your family's comfort and safety are too important to leave to chance. Let our 25+ years of North Georgia HVAC experience solve your pilot light problem permanently.
