What an automatic pilot light is and why it goes out

An automatic pilot light is a small flame that stays lit inside your furnace, water heater, or gas stove. Unlike older manual pilot lights that you light with a match, an automatic one reignites itself when the flame blows out—usually through a device called a thermocouple or electronic ignition system. When it fails to relight on its own, you may see a "pilot light out" warning on your appliance's display, or straightforward notice that your furnace won't turn on.

The most common reasons an automatic pilot light won't relight are a dirty pilot tube (which blocks gas flow), a faulty thermocouple that's no longer sensing the flame, a tripped safety valve, or a problem with the gas supply itself. Sometimes the issue is as straightforward as the gas being turned off at the control valve.

Key Takeaways

  • Always turn off the gas at the control valve and wait five minutes before attempting to relight an automatic pilot light.
  • Check that the gas supply valve is in the ON position and that the control knob is set to PILOT before you try to ignite.
  • Hold down the ignition button for 30 to 60 seconds while holding a lit lighter or match near the pilot tube opening.
  • If the pilot light stays lit after you release the button, turn the control knob to ON; if it goes out when ready, the thermocouple may need replacement.
  • If relighting fails after three attempts, turn the gas off and contact a technician—continuing to try can create a gas hazard.

Locate the pilot light assembly and control valve

Open the access panel or door on your appliance—usually a small metal cover on the front or side of the furnace, water heater, or stove. You'll see a small burner opening (the pilot tube) and nearby a control knob labeled with settings like OFF, PILOT, and ON. Some models also have a red ignition button next to the knob.

Find the gas control valve, which is a small lever or knob separate from the main control. It's typically located where the gas line enters the appliance. Make sure you can reach it easily before you start, because your first step is to turn it off.

Turn off the gas and wait

Turn the gas control valve to the OFF position. Wait a full five minutes. This clears any gas that may have accumulated inside the appliance and reduces the risk of a sudden ignition or explosion when you relight.

After five minutes, turn the gas control valve back to ON. Then turn the main control knob to PILOT (not ON). This setting allows gas to flow to the pilot tube only, not to the main burner.

Light the pilot and hold the ignition button

Hold a long lighter or long match near the pilot tube opening—the small hole where the flame should appear. At the same time, press and hold the red ignition button (or the control knob if it has a push-in ignition). Keep the button pressed for 30 to 60 seconds while the flame from your lighter or match is near the tube opening.

You should see a small blue flame appear at the pilot tube. Once it does, keep holding the ignition button for another 10 to 15 seconds to make sure the thermocouple heats up enough to sense the flame. Then release the button slowly.

Check whether the pilot light stays lit

Watch the pilot tube for the next 30 seconds. If the small blue flame stays steady, the pilot light has relit successfully. You can now turn the main control knob from PILOT to ON, which opens the gas to the main burner. Your furnace, water heater, or stove should now operate normally.

If the flame goes out as soon as you release the ignition button, the thermocouple is likely faulty and no longer sensing the flame. This is a common failure and requires a technician to replace the thermocouple—it's not a repair most homeowners can do safely.

What to do if relighting fails

If the pilot light won't stay lit after two or three attempts, stop trying. Turn the gas control valve to OFF and leave it off. Repeated attempts to ignite gas that isn't staying lit can create a dangerous buildup of unburned gas in the appliance.

The most likely culprits at this point are a faulty thermocouple, a clogged pilot tube, low gas pressure, or a problem with the electronic ignition system. All of these require a technician to diagnose and fix. Contact a licensed HVAC or appliance repair technician and describe what happened—that the pilot light won't relight or won't stay lit after relighting.

Common mistakes that prevent relighting

The biggest mistake is not waiting the full five minutes after turning off the gas. Skipping this step leaves unburned gas in the chamber, which can ignite suddenly or create a weak flame that the thermocouple can't sense. Another common error is turning the control knob all the way to ON instead of stopping at PILOT—this floods the appliance with gas and makes it harder to light the small pilot flame.

Many people also give up too quickly, releasing the ignition button before the thermocouple has had time to heat up. The button should stay pressed for at least 30 to 60 seconds. Finally, some people try to light the pilot with the gas valve in the OFF position, which prevents any gas from reaching the tube at all.

Frequently Asked Questions

How long should I hold the ignition button down?

Hold it for 30 to 60 seconds while the flame from your lighter or match is near the pilot tube opening. After the pilot light appears, keep the button pressed for another 10 to 15 seconds so the thermocouple can heat up and sense the flame. Releasing too early is a common reason the pilot light won't stay lit.

What if I smell gas while trying to relight the pilot?

Stop when ready and turn the gas control valve to OFF. Open windows and doors to ventilate the space. Do not use matches, lighters, or electrical switches. Wait 15 minutes, then call a technician. A strong gas smell usually means gas is leaking or accumulating, which is a safety hazard.

Can a dirty pilot tube prevent relighting?

Yes. A clogged pilot tube blocks gas flow, so even if you hold the ignition button down, no gas reaches the flame. You can try gently cleaning the tube opening with a thin wire or needle, but if that doesn't work, a technician can clean or replace it safely.

Is it safe to keep trying if the pilot light won't stay lit?

No. Stop after two or three attempts. Repeated tries allow unburned gas to build up inside the appliance, creating a fire or explosion hazard. Turn the gas off and contact a technician instead.

Why does my automatic pilot light keep going out?

The thermocouple is wearing out and no longer sensing the flame reliably, or the pilot tube is partially clogged. Both require a technician to fix. A thermocouple typically lasts 5 to 10 years before it needs replacement.