Water Heater Pilot Light Won't Stay Lit: Troubleshooting and Fix Guide

A gas water heater pilot light that keeps going out is one of the most common service calls I get. The good news is that it is rarely a serious problem. In about 80 percent of cases, the fix costs less than $20 and takes under 30 minutes.

The bad news is that a pilot light issue leaves you without hot water until you solve it. Nobody likes cold showers, so let’s get this diagnosed.

How the Pilot Light System Works

Before troubleshooting, it helps to understand what you are working with.

The pilot light is a small flame that burns continuously at the base of your gas water heater. Its job is to ignite the main burner when the thermostat calls for heat. A safety device called a thermocouple sits with its tip in the pilot flame. As long as the thermocouple senses heat, it sends a small electrical signal (measured in millivolts) to the gas control valve, telling it to keep the gas supply open.

When the pilot goes out, the thermocouple cools down within about 20 seconds and the electrical signal drops. The gas valve closes automatically, cutting off all gas flow. This is a critical safety feature that prevents raw gas from accumulating in your home.

So when your pilot won’t stay lit, something in this chain is failing: the flame itself, the thermocouple, the gas supply, or the gas valve.

Before You Start: Safety Rules

Gas work demands respect. Follow these rules:

1. If you smell gas strongly, do not attempt any repairs. Leave the house immediately and call your gas utility from outside. Do not flip any switches or use your phone inside the house.
2. Work in a well-ventilated area. Open a window or door to the room if possible.
3. Keep a fire extinguisher accessible.
4. Never use an open flame to check for gas leaks. Use soapy water on connections instead.

For a full overview, check our water heater safety guide.

Cause 1: Dirty or Misaligned Thermocouple

This is the most common cause of a pilot light that won’t stay lit. If the thermocouple tip is coated with soot, carbon, or corrosion, it cannot generate enough voltage to keep the gas valve open. If it has been bumped or bent away from the pilot flame, it does not get hot enough to produce a signal.

How to Fix It

1. Turn the gas control to “Off” and let everything cool for 10 minutes.
2. Locate the thermocouple. It is a thin copper tube that runs from near the pilot flame to the gas control valve.
3. Follow it to the tip, which sits in or near the pilot flame.
4. Clean the tip with fine-grit sandpaper (220 grit works well) or steel wool. Remove any soot, carbon, or white oxidation.
5. Check the position. The tip should be directly in the pilot flame, fully engulfed. If it is sitting beside the flame or below it, gently bend the thermocouple bracket so the tip sits in the top third of the flame.
6. Relight the pilot and hold the button for a full 60 seconds before releasing.

Cost: Free. Time: 15 minutes.

Cause 2: Failed Thermocouple

Thermocouples are wear items. They last 5 to 10 years on average and then stop generating enough millivolts to keep the gas valve open. If cleaning and repositioning did not fix the problem, the thermocouple has worn out.

How to Fix It

1. Turn the gas control to “Off.”
2. Disconnect the thermocouple from the gas control valve. It threads into a brass fitting on the bottom of the valve. Use a small wrench (usually 7/16 inch) to unscrew it.
3. Remove the thermocouple from its bracket at the burner assembly.
4. Take the old thermocouple to a hardware store for a match, or buy a universal thermocouple. Universal models fit most residential water heaters and cost $12 to $20.
5. Install the new thermocouple in reverse order. Thread it finger-tight into the gas valve, then snug with a wrench. Do not overtighten, as the brass fitting strips easily.
6. Position the tip in the pilot flame and relight.

Cost: $12 to $20 for the part. Time: 20 to 30 minutes.

After replacing the thermocouple, this is a good time to also check whether your anode rod needs attention since you are already working on the heater.

Cause 3: Clogged Pilot Tube

The pilot tube is the small gas line that feeds the pilot flame. It can clog with dust, lint, spider webs, or debris, especially in garages, basements, or workshops. A partially clogged pilot tube produces a weak, small flame that cannot heat the thermocouple adequately.

How to Identify It

• The pilot flame is small, yellow, or wavering instead of a steady, sharp blue cone
• The pilot lights but produces a flame less than half an inch tall
• The pilot goes out within 30 seconds of releasing the control button

How to Fix It

1. Turn gas to “Off” and wait 10 minutes.
2. Locate the pilot tube. It is a thin aluminum or copper tube that runs from the gas valve to the burner assembly.
3. Find the pilot orifice (the tiny opening where gas exits to create the pilot flame).
4. Use a sewing needle or thin wire to carefully clear the orifice. Do not ream it wider.
5. Blow compressed air through the tube to clear any debris further back.
6. Reassemble and relight.

Cost: Free. Time: 15 to 20 minutes.

Cause 4: Drafts and Air Currents

Strong drafts can blow out the pilot light, especially in garages, open basements, or rooms near HVAC return vents. The draft hood on top of the water heater is designed to prevent downdrafts through the flue from reaching the pilot, but it cannot handle cross-drafts or strong competing airflows.

How to Identify It

• The pilot goes out at random intervals, not immediately after lighting
• It happens more often when doors or windows are open, or when exhaust fans (kitchen, bathroom, dryer) are running
• The flame visibly flickers or leans to one side

How to Fix It

• Identify the draft source. Stand near the water heater and hold a lit match. Watch which direction the flame leans.
• Seal gaps, close windows, or redirect the airflow away from the heater.
• Make sure the draft hood on top of the heater is properly seated and not damaged.
• Verify that your home has adequate combustion air. Gas water heaters in enclosed rooms need fresh air vents to the outside, typically two louvers in the door or wall.

If competing exhaust appliances are the issue (a powerful range hood pulling air down the water heater flue), the solution may require a professional to install a power vent or reroute the flue.

Cause 5: Faulty Gas Control Valve

If you have ruled out the thermocouple, pilot tube, and drafts, the gas control valve itself may be defective. The valve contains an electromagnet that the thermocouple energizes. If the electromagnet fails, it cannot hold the valve open regardless of the thermocouple signal.

How to Identify It

• A brand new thermocouple does not fix the problem
• The pilot tube is clear and the flame is strong
• No drafts are present
• You can hear a clicking sound when the valve releases immediately after you let go of the pilot button

How to Fix It

Gas valve replacement is a job for a licensed technician. The valve is an integral part of the gas system, and improper installation creates a serious leak hazard.

A gas valve typically costs $150 to $250 for the part, plus $100 to $200 in labor. On a water heater older than 8 years, this repair often does not make financial sense compared to full replacement. Read our DIY vs. plumber decision guide for help with that call.

Cost: $200 to $400 installed.

Cause 6: Insufficient Gas Pressure

Low gas pressure from the supply line can produce a weak pilot flame that cannot sustain the thermocouple signal. This is less common but happens in homes where multiple gas appliances run simultaneously (furnace, stove, fireplace, dryer) and the gas meter or supply line is undersized.

How to Identify It

• The pilot goes out when other gas appliances kick on
• The pilot flame is consistently weak regardless of thermocouple or orifice condition
• Other gas appliances also seem to underperform (low burner flames on the stove, slow furnace heat-up)

How to Fix It

Gas pressure testing requires a manometer and should be done by a licensed technician or your gas utility. The incoming pressure should be 7 inches of water column (WC) for natural gas. If it is low, the gas company may need to adjust the regulator at the meter, or the supply line may need upsizing.

How to Relight the Pilot Light

Once you have addressed the root cause, here is the standard relighting procedure:

1. Turn the gas control knob to “Off.” Wait 5 minutes for any residual gas to dissipate.
2. Turn the knob to “Pilot.”
3. Press and hold the pilot button (or press and hold the knob, depending on the model).
4. While holding the button, click the igniter button or hold a long fireplace match at the pilot opening.
5. Once the pilot lights, continue holding the button for 60 seconds. This gives the thermocouple time to heat up.
6. Release the button slowly. The pilot should stay lit.
7. Turn the gas control knob to your desired temperature setting.
8. The main burner should fire within a minute or two as the thermostat calls for heat.

If the pilot goes out immediately after you release the button, the thermocouple is not getting hot enough. Re-read Causes 1 through 3 above.

When to Replace Instead of Repair

The pilot light system is simple and most repairs are inexpensive. But there are situations where the smarter move is a new water heater:

• The unit is over 10 years old and the gas valve has failed
• You are chasing multiple simultaneous issues (pilot problems plus sediment noise plus rusty water)
• The repair cost exceeds half the price of a new unit
• You want to switch to a tankless system anyway

Related Guides

• Water Heater Safety Guide, All 7 hazards to watch for
• Water Heater Pilot Light Troubleshooting, Broader pilot light coverage
• Water Heater Repair: DIY vs. Plumber, When to call in a pro
• Water Heater Noise Troubleshooting, Diagnosing other common issues
• When to Replace Your Anode Rod, Maintenance while you are working on the heater

Sources

• Honeywell Gas Valve Documentation, Thermocouple specifications and pilot system operation
• A.O. Smith Water Heater Troubleshooting, Manufacturer diagnostic procedures
• National Fuel Gas Code (NFPA 54), Safety standards for gas appliance maintenance