Why Does My Pilot Light Keep Going Out? Causes and Fixes

A pilot light that keeps going out is usually caused by a dirty or worn thermocouple, the small metal rod that sits in the pilot flame and tells the gas valve the flame is on. If it cannot sense heat, it shuts off the gas for safety. Cleaning it or replacing it fixes most cases, and the part costs about $15 to $25.

Other causes include drafts, a clogged pilot opening, and a gas supply problem. Here is how to find yours, relight it safely, and know when to call a pro.

What a pilot light does

Many older gas water heaters, furnaces, boilers, fireplaces, and ovens have a pilot light, a small flame that stays lit all the time. When the appliance needs heat, the main burner lights from that small flame.

A safety part called a thermocouple sits in the pilot flame. The flame heats the tip, which makes a tiny bit of electricity. That signal tells the gas valve to stay open. If the flame goes out, the signal stops, the valve closes, and the gas shuts off. That is how the system stops gas from filling your home.

So a pilot that "keeps going out" is often not a problem with the flame. It is a problem with the safety system that watches the flame.

The most common causes

1. A dirty thermocouple

Soot and rust can cover the tip. A coated tip cannot sense the heat well, so the valve closes even though the pilot is burning. This is the most common reason the flame will not stay lit.

2. A worn or bad thermocouple

Thermocouples wear out over time. Even a clean one can stop making enough signal after many years. If the pilot lights, stays on while you hold the button, and goes out a few seconds after you let go, a weak thermocouple is a top suspect.

3. A thermocouple that is out of position

The tip must sit in the flame, with the flame touching the top inch or so. If it was bumped, bent, or loosened, it may not get enough heat.

4. A dirty pilot opening

Dust and lint can clog the tiny pilot tube. The flame gets weak, small, and yellow instead of strong and blue. A weak flame cannot heat the thermocouple well.

5. Drafts

A gust from a vent, a window, or a door can blow out the pilot. Look at where the heater sits. Did something change, such as a new exhaust fan, a window left open, or a new vent pipe?

6. A gas supply or valve problem

If the gas pressure is low, or the gas control valve is failing, the flame may be weak or go out. These are jobs for a licensed pro.

What the flame should look like

A healthy pilot flame is mostly blue, steady, and about an inch tall, wrapping the tip of the thermocouple. Watch it for a moment:

A yellow flame can also point to incomplete burning, which can make carbon monoxide. Make sure you have working carbon monoxide alarms near sleeping areas. Our guide on smoke and CO alarm care explains alarm care, including combination alarms.

How to relight a water heater pilot light

Steps differ by model, so follow the label on your heater first. This is the usual process for a gas water heater:

1. Turn the thermostat knob to "pilot" or "off."
2. Wait about 5 minutes so any leftover gas clears.
3. Smell for gas. If you smell it, stop and leave.
4. Remove the access cover near the bottom of the heater.
5. Turn the knob to "pilot" and press and hold it down.
6. Light the pilot by pressing the igniter button, or by holding a long lighter near the pilot opening.
7. Keep holding the knob down for 30 to 60 seconds. This lets the thermocouple heat up.
8. Release the knob slowly. The flame should stay lit.
9. Turn the knob to "on" and set the temperature.
10. Replace the cover.

If the pilot goes out after you let go, hold the knob longer, up to about a minute, and try again. If it still goes out after two or three tries, stop and move on to the fixes below. Do not keep trying again and again.

How to clean a thermocouple

Do this only if you are comfortable working with gas appliances.

1. Turn the gas valve to "off" and let the appliance cool for at least 5 minutes.
2. Turn off power to a furnace or boiler if it has a power switch.
3. Find the thermocouple. It is a thin copper rod beside or in front of the pilot flame.
4. Wipe off soot. Use a piece of fine emery cloth, steel wool, or a scouring pad. Rub lightly. The part is fragile.
5. Wipe it clean with a dry cloth.
6. Check that the tip sits in the flame and that the nut that holds it is snug, but not over-tight.
7. Relight the pilot using the steps above.

Never use water or spray cleaner on the part while the gas is on.

How to replace a thermocouple

If cleaning does not help, replace it. Thermocouples are sold by length and fit, so match the part number on yours or take the old one to the store.

1. Turn off the gas and let everything cool.
2. Unscrew the nut that holds the thermocouple to the gas control valve.
3. Remove the other end from its bracket near the pilot.
4. Put the new one in, then tighten the nut by hand, plus a quarter turn with a wrench.
5. Relight the pilot and check that the flame wraps the tip.

The part costs about $15 to $25. If you hire a pro, expect roughly $150 to $250 for the visit and the part, though prices vary by region.

If the pilot stays on but you get no heat or hot water

Sometimes the pilot burns fine and the problem is somewhere else:

• Water heater with no hot water. Check that the thermostat knob is set to a warm setting, not "pilot." If you also hear loud popping, read why a noisy water heaters.
• Furnace blowing cold air. A cold blast with the pilot on can mean a dirty filter or a limit switch problem. See why a furnace blows cold.
• Smell when you first start the furnace. A dusty smell is normal in fall. See what a burning smell means when the heat turns on.

Do I have a pilot light at all?

Many newer appliances do not use a standing pilot. They use an electronic ignition that lights the burner only when the appliance calls for heat.

• Water heaters with a small window and a red or black push button usually have a standing pilot.
• Furnaces made in the last 20 years or so mostly use electronic ignition.
• Gas stoves with a clicking sound use an igniter. If yours keeps clicking, read about why a gas stove keeps clicking.

If your appliance has electronic ignition, a "pilot that goes out" is really an igniter or flame sensor problem. The fix is similar, but the parts are different, so check the manual or call a technician.

Is it safe to keep relighting it?

Relighting once or twice is fine if there is no gas smell. But a pilot that keeps going out is telling you something is wrong. Do not keep relighting it over and over. Instead:

• Check for gas odor each time before you light it.
• Make sure carbon monoxide alarms work.
• Find the cause, or call a pro.

When to call a professional

Call a licensed gas technician if:

• You smell gas at any time. Leave first and call from outside.
• The pilot goes out again within a day after cleaning or replacing the thermocouple.
• The flame is yellow or orange, or it makes a soot stain around the heater.
• The heater is more than 10 to 15 years old. It may be time to replace the whole unit.
• You see rust, water, or scorch marks around the appliance.
• Your carbon monoxide alarm sounds.
• You are not sure how to do any step. It is always okay to ask for help with gas.

Prevent it from happening again

• Have your furnace and water heater checked once a year, ideally in early fall.
• Keep the area around the appliance clear of dust, boxes, and anything that can burn.
• Vacuum around the base now and then to keep lint away from the pilot opening.
• Test carbon monoxide alarms every month and replace them as the label says.
• Watch for drafts from new windows, vents, or exhaust fans.

The bottom line

A pilot light that keeps going out is usually caused by a dirty or worn thermocouple. Turn off the gas, clean the tip gently with emery cloth, and relight the pilot while holding the knob for a full 30 to 60 seconds. If it still goes out, replace the thermocouple for about $15 to $25, or call a pro for about $150 to $250. If you ever smell gas, leave the house and call your gas company right away.