A pilot light that won’t stay lit almost always points to a faulty thermocouple. In most cases, that’s a repair, not a replacement. But the right answer depends on your furnace’s age, the frequency of the problem, and what else the diagnostic turns up.

How a Pilot Light System Actually Works

Before diagnosing the problem, it helps to understand the mechanism. A standing pilot light is a small, continuously burning flame found in older gas furnaces, water heaters, and boilers. Its job is twofold: ignite the main burner when the thermostat calls for heat, and prove to the gas valve that a flame is present before allowing gas to flow.

The component that does the “proving” is called the thermocouple. It’s a simple safety device: a metal probe that sits in the pilot flame and generates a small electrical current (around 25 to 30 millivolts) when heated. That current signals the gas valve to stay open. When the flame goes out, the current drops, the gas valve closes, and gas flow stops automatically.

This system is a safety feature, not a flaw. If your pilot keeps going out, the safety system is working exactly as designed. The question is what’s causing it to shut down.

What Causes a Pilot Light to Keep Going Out?

The most common causes, in order of frequency, are listed below.

Is the Thermocouple Worn or Faulty?

The thermocouple is the single most common reason a pilot light repeatedly extinguishes. These components wear out over time. As the metal probe degrades, it generates less current, and eventually produces insufficient voltage to keep the gas valve open, even when the flame is burning normally.

A functioning thermocouple should generate at least 20 to 25 millivolts. A technician can test this with a multimeter while the pilot is lit. Readings below 20 mV indicate a thermocouple that needs replacement.

Thermocouple replacement is a straightforward repair that typically costs $75 to $200 including parts and labor. The part itself costs $10 to $25 at most hardware stores.

Is the Thermocouple Positioned Incorrectly?

Even a functional thermocouple fails if it’s not positioned correctly in the pilot flame. The tip must be enveloped by the flame, not just adjacent to it. If someone recently serviced the furnace and the pilot light problem started shortly after, thermocouple repositioning is worth checking before replacement.

Is There a Draft or Airflow Problem?

In Oklahoma, where wind and pressure differentials can be significant, drafts through flue vents, unsealed utility penetrations, or gaps around furnace doors can extinguish a pilot flame repeatedly. This is more common in older homes with naturally drafty basements or utility closets.

If the pilot goes out primarily on windy days or when exterior doors open, draft infiltration is the likely culprit rather than the thermocouple itself.

Is the Gas Valve Failing?

The main gas valve contains an internal safety seat that is held open by the thermocouple current. When this seat wears or the valve internals degrade, it may not hold open reliably even with adequate thermocouple voltage. Gas valve replacement is more expensive ($150 to $400 or more in parts alone) and typically pushes the repair-vs-replace calculation toward replacement in older equipment.

Is the Pilot Orifice Clogged?

The pilot orifice is a small port that meters gas flow to the pilot burner. Dust, rust particles, or debris can partially restrict this orifice, producing a weak flame that doesn’t fully engulf the thermocouple tip. A weak pilot flame looks yellow or orange rather than a crisp blue. Cleaning or replacing the orifice is a low-cost fix.

Repair vs. Replace: How to Decide

The pilot light itself is rarely the reason to replace a furnace. It’s what the pilot light problem reveals about the overall system that matters.

Here’s a practical framework:

The industry standard guidance from ENERGY STAR and most HVAC trade organizations is to consider replacement when a system is over 15 years old and repair costs exceed 50% of the cost of a new system. In Oklahoma’s climate, where heating systems run hard through November to March and often serve homes with higher-than-average square footage, that threshold is a reasonable guide.

Does a Pilot Light Problem Indicate Anything Dangerous?

In some cases, yes. A pilot light that goes out is not inherently dangerous because the thermocouple safety system prevents unburned gas from accumulating. However, the diagnostic process matters.

A cracked heat exchanger is the most serious finding that can accompany pilot light service. Heat exchangers develop cracks over time due to thermal stress. A cracked exchanger can allow combustion gases, including carbon monoxide, to mix with circulated air. Heat exchanger failure is not detectable without a proper inspection, which is one reason pilot light service calls should always include a visual inspection of the burner assembly and heat exchanger.

If you smell gas near your furnace at any point, do not attempt to relight the pilot. Leave the home, leave the door open, and call your gas utility or 911 from outside.

The Consumer Product Safety Commission (CPSC) estimates that carbon monoxide poisoning from heating equipment injures thousands of people annually in the United States. Working CO detectors on every floor of an Oklahoma home are not optional.

Does a Pilot Light Problem Indicate Anything Dangerous?

For most homeowners, yes. Relighting a pilot light is a task you can perform safely following the manufacturer’s instructions printed on the furnace door panel.

The general sequence is: turn the gas valve knob to “off” and wait five minutes to allow any residual gas to dissipate, then turn to “pilot,” press and hold the reset button while applying a lighter to the pilot burner, hold the reset button for 30 to 60 seconds after the flame catches to allow the thermocouple to heat up, then slowly release and turn the knob to “on.”

If the pilot won’t stay lit after two or three attempts following this procedure, stop and call a technician. Repeated unsuccessful relighting attempts without diagnosis can mask an underlying issue.

What If My Furnace Has Electronic Ignition Instead?

Many furnaces installed after 1990 use electronic ignition rather than a standing pilot light. These systems use either a hot surface ignitor (a ceramic element that glows red-hot) or an intermittent pilot ignitor (a spark ignitor that lights a temporary pilot, which then lights the main burner).

If your furnace has no pilot light to relight and simply fails to ignite when the thermostat calls for heat, the system almost certainly has electronic ignition. The diagnostic process is different, and the components involved (ignitor, flame sensor, control board) differ from pilot light systems.

The flame sensor in an electronic ignition furnace plays a similar role to the thermocouple in a standing pilot system. It confirms flame presence before allowing gas to flow, and it fails in similar ways. Gradual degradation of the sensor rod causes intermittent ignition failures, particularly during cold snaps when the system is running most.

How Often Should a Gas Furnace Be Inspected in Oklahoma?

Once per year, before heating season begins. October is the right window for Oklahoma homeowners, after the cooling season ends and before the first cold front arrives.

Annual inspection should include: burner condition, heat exchanger inspection, thermocouple or flame sensor testing, flue and draft check, filter replacement, and electrical component review. The National Fire Protection Association (NFPA) and the American Gas Association both recommend annual professional service for gas- fired heating equipment.

Homeowners who skip annual service are statistically more likely to experience mid- season breakdowns, which in Oklahoma can mean emergency service calls during ice storms or periods of sustained below-freezing temperatures.

Pilot Light vs. Electronic Ignition: Key Differences

FAQ: Pilot Light Problems

Why does my pilot light keep going out after I relight it?

The most common cause is a failing thermocouple. The pilot lights successfully but the thermocouple isn’t generating enough current to hold the gas valve open, so the flame extinguishes within seconds to minutes of releasing the reset button. Testing with a multimeter confirms this quickly.

How long should a thermocouple last?

A thermocouple typically lasts 7 to 10 years under normal operating conditions. In Oklahoma, where furnaces run intensively during heating season, toward the lower end of that range is common.

Is it safe to keep relighting a pilot light that keeps going out?

It’s safe to attempt relighting following the manufacturer’s procedure, provided you wait the recommended time between attempts to allow gas to clear. However, if the pilot won’t stay lit after two or three attempts, repeated relighting without resolving the root cause accomplishes nothing and warrants a service call.

My furnace is 20 years old and the pilot keeps going out. Should I repair or replace?

At 20 years, you’re at the end of the typical service life for residential gas furnaces. A thermocouple replacement is inexpensive enough to be worth doing even on older equipment, but the technician visit should include a full system evaluation. If the heat exchanger, gas valve, or other major components show wear, replacement likely makes more economic sense than continued repairs.

Does a pilot light going out mean there’s a gas leak?

Not necessarily. The thermocouple safety system is designed to shut off gas when the pilot extinguishes, which it does reliably. However, if you smell gas near the furnace, do not attempt to diagnose or relight it. Evacuate and call your gas utility.

What does a healthy pilot flame look like?

A properly burning pilot flame is crisp and blue, with a small inner cone. A weak, yellow, or orange pilot flame indicates insufficient gas flow, a dirty orifice, or draft interference, all of which can prevent the thermocouple from reaching operating temperature.

The Bottom Line

A pilot light that won’t stay lit is almost always a thermocouple problem, a repair that costs under $200 and takes a technician under an hour to complete. The decision to repair or replace depends on the furnace’s age, what else the technician finds during the service visit, and whether the repair cost clears the 50% threshold relative to replacement.

What a pilot light problem should always trigger is a professional inspection. The flame you can see is easy to fix. What matters more is what the technician finds while they’re in there.

Pilot Light Won’t Stay Lit? Patton Air Knows Exactly What to Look For.

A pilot light that keeps going out is your furnace telling you something is wrong. It might be a quick thermocouple swap. It might be something that needs a closer look. Either way, the worst move is to keep relighting it and hoping it holds.

The team at Patton Air has been diagnosing and servicing gas furnaces across Kiefer, Sapulpa, and the Tulsa Metro for 45+ years. We’ve handled every variation of this problem, from a simple thermocouple replacement to heat exchanger inspections that revealed something more serious. We give you a straight answer, upfront pricing, and the repair done right.

If your pilot light is giving you trouble or your furnace hasn’t had a proper inspection before this heating season, don’t wait for a cold night to find out there’s a bigger issue underneath.

Call us at 918-245-9346 or email [email protected]

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