How to Fix a Gas Fireplace Pilot Light That Won't Stay Lit

By GasFireplaceFixer.com · Gas Fireplace Repair Guide

⚠ Safety First: Always shut off the gas supply valve before performing any hands-on maintenance. If you smell gas at any time, evacuate immediately and call your gas utility. These guides are for informational purposes — if you are unsure at any point, stop and contact a certified technician.

A pilot light that refuses to stay lit is the most common gas fireplace complaint — and the good news is it's usually a straightforward fix you can handle yourself. This guide walks you through every likely cause and the exact steps to resolve it.

Why Does a Gas Fireplace Pilot Light Go Out?

The pilot flame is kept alive by a small copper rod called a thermocouple (or thermopile on millivolt systems). When the pilot flame heats this rod, it generates a tiny electrical current that tells the gas valve to stay open. If that current drops below the threshold — whether from a dirty rod, misaligned flame, or a failing component — the gas valve shuts off as a safety measure and the pilot goes out.

Step 1: Clean the Thermocouple

Turn the gas valve to OFF and wait 5 minutes. Locate the thermocouple — a thin copper rod positioned directly in the pilot flame path. Using 400-grit emery cloth, gently sand away any oxidation or carbon buildup from the tip. Wipe clean with a dry cloth. This alone fixes the problem in roughly 40% of cases.

Step 2: Reposition the Thermocouple

The thermocouple tip must be fully engulfed by the pilot flame — not just adjacent to it. If the tip is only catching the edge of the flame, bend the mounting bracket slightly so the tip sits deeper inside the flame. Even a small repositioning makes a significant difference in the millivolt output.

Step 3: Check the Connections

Trace the thermocouple lead wire down to the gas valve. Unscrew the connector, inspect for corrosion, and reseat it finger-tight plus a quarter turn with pliers. A loose or corroded connection is a common cause of intermittent pilot outages.

Step 4: Test the Millivolt Output

If the pilot still won't hold after the above steps, test the thermocouple with a multimeter set to DC millivolts. A healthy thermocouple reads 25–35 mV. A thermopile reads 300–750 mV. Anything below threshold means the component needs replacement. Replacement thermocouples cost $12–20 at most hardware stores.

Step 5: Replace the Thermocouple

Unscrew the old thermocouple from the gas valve and the pilot assembly bracket. Take it to a hardware store to match the length and thread type. Install the new one, hand-tighten the connection, relight the pilot per your manufacturer's instructions, and test. Most replacements take under 30 minutes.

When to Call a Professional

If you've replaced the thermocouple and the pilot still won't hold, the issue is likely a failing gas valve or a problem with the main control module. These repairs require a licensed technician with proper tools and certifications. Don't attempt gas valve repairs yourself.

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