Few things are more frustrating than a gas fireplace pilot light that refuses to stay lit. You hold down the pilot knob, the flame appears, but the moment you release it — the pilot goes out. This is one of the most common gas fireplace problems homeowners face, and the good news is that the cause is usually a simple, inexpensive part that you can replace yourself.

In this guide, we'll walk through every common cause of a pilot light that won't stay lit, explain how each component works, and point you toward the right replacement parts.

How a Gas Fireplace Pilot System Works

Before diving into troubleshooting, it helps to understand the basic components involved in keeping your pilot light burning:

• Pilot assembly — The burner that produces the small pilot flame. It includes the pilot hood, orifice, and mounting bracket.
• Thermocouple — A safety sensor that detects the pilot flame. It generates a small electrical voltage (measured in millivolts) when heated by the flame. This voltage holds the gas valve open.
• Thermopile — Similar to a thermocouple but generates a higher voltage (typically 250-750 millivolts). Used in millivolt systems to power the gas valve and, in some cases, a wall switch or remote receiver.
• Gas valve — The main control valve that regulates gas flow to both the pilot and main burner. It uses the signal from the thermocouple or thermopile to stay open.

When the pilot is lit, the thermocouple or thermopile heats up and generates voltage. This voltage creates an electromagnetic field inside the gas valve that holds it open. If the pilot goes out, the voltage drops, the magnet releases, and the valve closes — preventing unburned gas from flowing into your home.

Cause #1: A Faulty Thermocouple

The thermocouple is the single most common reason a pilot light won't stay lit. Over time, thermocouples degrade from constant heat exposure. The junction tip oxidizes, corrosion builds up on the connection, and the millivolt output drops below the threshold needed to hold the gas valve open.

Symptoms of a Bad Thermocouple

• Pilot lights when you hold the knob down but goes out within 5-30 seconds of releasing
• The thermocouple tip appears discolored, cracked, or corroded
• A multimeter reading shows less than 20 millivolts (most need 25+ mV to work reliably)

The Fix

Thermocouple replacement is one of the simplest gas fireplace repairs. Most thermocouples are held in place with a single nut at the gas valve and a bracket clip at the pilot assembly. You can typically complete the replacement in 15-20 minutes with just a wrench.

Browse our full selection of gas fireplace thermocouples to find the right replacement for your unit. We carry universal-fit thermocouples as well as OEM replacements for major brands.

Cause #2: A Weak Thermopile

If your fireplace uses a millivolt gas valve system (common in most gas fireplaces manufactured after the 1990s), the thermopile is the power source that keeps everything running. A thermopile is essentially a series of thermocouples bundled together to produce higher voltage.

Symptoms of a Failing Thermopile

• Pilot stays lit, but the main burner won't ignite from the wall switch or remote
• Pilot light is inconsistent — sometimes stays on, sometimes doesn't
• Open-circuit voltage reads below 300 millivolts when tested with a multimeter
• Closed-circuit voltage (under load) drops below 150 millivolts

How to Test a Thermopile

1. Light the pilot and let it burn for at least 2 minutes to fully heat the thermopile.
2. Set your multimeter to DC millivolts.
3. Disconnect the thermopile leads from the gas valve.
4. Measure the open-circuit voltage across the two leads. You should see 300-750 mV.
5. Reconnect the leads and measure voltage at the gas valve terminals (closed-circuit). You should see at least 150 mV.

If your readings are low, it's time for a replacement. Check out our gas fireplace thermopiles for compatible options.

Cause #3: Dirty or Misaligned Pilot Assembly

Even with a perfectly good thermocouple and thermopile, a dirty or misaligned pilot assembly can cause the pilot to go out. The pilot flame must directly contact the thermocouple tip — if it doesn't, the sensor can't generate enough voltage.

Common Pilot Assembly Issues

• Clogged pilot orifice — Dust, spider webs, and debris can partially block the tiny orifice, producing a weak, yellow flame instead of a strong blue one.
• Misaligned pilot hood — If the hood is bent or shifted, the flame may not reach the thermocouple or thermopile properly.
• Carbon buildup — Over years of use, carbon deposits accumulate on the pilot assembly components, reducing flame quality.

The Fix

You can try cleaning the pilot orifice with compressed air and a fine wire or needle. However, if the assembly is old and corroded, replacement is usually the better option. A new pilot assembly ensures proper flame pattern and reliable contact with the thermocouple.

We stock a wide range of gas fireplace pilot assemblies for all major brands and ignition types.

Cause #4: Draft or Air Supply Issues

External factors can also extinguish your pilot light:

• Downdrafts — Wind blowing down the chimney or vent can extinguish the pilot, especially in direct-vent or B-vent fireplaces.
• Exhaust fan interference — Bathroom fans, kitchen range hoods, or dryer vents near the fireplace can create negative pressure that pulls the pilot flame away from the thermocouple.
• Sealed glass gasket failure — In direct-vent fireplaces, the glass front creates a sealed combustion chamber. If the gasket around the glass deteriorates, outside air can disrupt the pilot.

The Fix

Check your vent termination cap outside for blockage or damage. Make sure exhaust fans aren't running when you're trying to light the pilot. Inspect the glass door gasket and replace it if it's worn or compressed.

Cause #5: Gas Valve Problems

Less commonly, the gas valve itself can be the problem. The electromagnet inside the valve that responds to the thermocouple signal can weaken over time, requiring a higher voltage to stay engaged.

Signs of a Gas Valve Issue

• New thermocouple and thermopile installed, but pilot still won't hold
• Thermocouple/thermopile millivolt readings are within spec, but valve won't stay open
• Gas valve makes a clicking sound when it drops out

Gas valve replacement is more involved than replacing a thermocouple, but it's still within reach for a handy homeowner. Visit our gas fireplace gas valves collection to find the right valve for your fireplace model.

Troubleshooting Flowchart

Follow this step-by-step process to diagnose the issue:

1. Light the pilot and hold the knob for 60 seconds. This gives the thermocouple/thermopile time to heat up fully.
2. Release the knob slowly. If the pilot goes out immediately, the thermocouple is likely the issue.
3. If the pilot stays lit, try turning on the main burner. If the burner won't light, the thermopile may be weak.
4. Inspect the pilot flame. It should be blue with a small yellow tip, and it must be touching the thermocouple. If it's weak or yellow, clean or replace the pilot assembly.
5. Test with a multimeter. This is the most reliable diagnostic step. Measure thermocouple voltage (should be 25+ mV) and thermopile voltage (should be 300+ mV open circuit).

When to Call a Professional

While most pilot light issues are DIY-friendly, you should call a qualified gas fireplace technician if:

• You smell gas when the fireplace is off
• The gas valve is leaking
• You're not comfortable working with gas appliances
• You've replaced the thermocouple, thermopile, and pilot assembly and the problem persists
• Your fireplace has an electronic ignition system that requires specialized diagnostics

Always follow manufacturer instructions and local building codes when performing repairs. Turn off the gas supply before working on any gas fireplace components.

Find the Right Replacement Parts

At Fireplace Choice, we carry replacement parts for all major gas fireplace brands including Heat N Glo, Heatilator, Napoleon, Empire, Superior, and more. Whether you need a thermocouple, thermopile, pilot assembly, or gas valve, we have the parts you need to get your fireplace working again.

Not sure which part you need? Contact our team for help identifying the right component for your specific fireplace model.