Lighting the Pilot Light: The Basic Steps

To light the pilot on an A.O. Smith water heater, you turn the gas control knob to "Pilot," hold down the ignition button while holding a lit match or lighter to the pilot burner opening, and keep the button pressed for 30 to 60 seconds after the flame catches. Once the pilot stays lit on its own, turn the gas control knob to "On" and listen for the main burner to ignite within a few seconds.

The entire process takes about two minutes. If the pilot won't stay lit after you release the button, the thermocouple (a safety sensor) may need cleaning or replacement. Most homeowners can do this themselves with basic tools.

Key Takeaways

  • Turn the gas control knob to "Pilot," press and hold the ignition button, and use a match or lighter to ignite the small flame at the pilot opening.
  • Keep the ignition button pressed for 30 to 60 seconds after the pilot flame appears so the thermocouple heats up and signals the gas valve to stay open.
  • If the pilot goes out when ready after you release the button, the thermocouple is likely dirty or failing and should be cleaned or replaced.
  • A.O. Smith heaters have the gas control knob and ignition button on the front of the control box, usually near the bottom of the tank.

Locate the Control Box and Gas Knob

On an A.O. Smith water heater, the control box is mounted on the outside of the tank, typically near the bottom. You will see a round knob labeled with settings like "Off," "Pilot," and "On." Next to or below this knob is a red or black button labeled "Ignition" or sometimes just a small push button.

Before you start, make sure the area around the heater is clear and well-ventilated. If you smell gas before you begin, do not attempt to light the pilot. Leave the area, open windows, and call your gas company's emergency line.

Turn the Knob to Pilot and Press the Ignition Button

Rotate the gas control knob clockwise until it points to "Pilot." You should hear a faint hiss as gas begins to flow to the pilot burner. Now press and hold the ignition button. You may hear clicking sounds as the igniter attempts to spark, or you may see a small spark near the pilot opening.

If the igniter does not spark after five to ten seconds of clicking, release the button and try again. Some A.O. Smith models have an igniter that works only a few times before needing a rest. If clicking continues without a spark, the igniter battery may be dead or the igniter itself may have failed.

Light the Pilot Flame with a Match or Lighter

While holding the ignition button down, bring a lit match or long lighter to the small opening where the pilot flame should appear. This opening is usually a small hole or tube pointing downward near the bottom of the burner assembly. You should see a small blue flame ignite within a few seconds.

Keep the match or lighter in place for a moment to make sure the flame is steady, then remove it. The pilot flame should be about the size of a match head and burn with a steady blue color. If the flame is yellow or orange, the burner may be dirty, but it will still work for now.

Hold the Button Down for 30 to 60 Seconds

Once the pilot flame is burning, continue holding the ignition button down for at least 30 seconds, and up to 60 seconds. During this time, the thermocouple—a small metal rod in the pilot flame—is heating up. When it reaches the right temperature, it sends a signal to the gas valve that tells it to stay open even after you release the button.

If you release the button too early, the pilot flame will go out because the thermocouple has not warmed up enough. Thirty seconds is usually enough, but if the pilot goes out right after you release the button, try again and hold it for the full 60 seconds.

Turn the Knob to On and Check the Main Burner

After holding the button for 30 to 60 seconds, slowly release it while watching the pilot flame. The flame should stay lit. Now rotate the gas control knob counterclockwise to "On." Within a few seconds, you should hear a soft whoosh as the main burner ignites. The burner should produce a blue flame that fills the combustion chamber.

If the main burner does not ignite within 10 seconds, turn the knob back to "Off," wait a minute, and try again. If it still does not light, the thermocouple may be faulty or the main burner may be blocked with debris.

Troubleshooting When the Pilot Won't Stay Lit

The most common reason a pilot light goes out when ready after you release the ignition button is a dirty thermocouple. The thermocouple is a thin metal rod that sits in the pilot flame. When it gets coated with dust or soot, it cannot sense the heat from the flame and tells the gas valve to close.

To clean the thermocouple, turn the gas knob to "Off" and wait five minutes for any remaining gas to clear. Locate the thermocouple—it is the thin metal rod running into the pilot flame area. Use fine-grit sandpaper or a small wire brush to gently scrub the tip of the rod until it is shiny. Wipe away any dust with a clean cloth, then try lighting the pilot again.

If cleaning does not work, the thermocouple may have failed internally and will need to be replaced. A.O. Smith thermocouples are inexpensive (usually under $20) and can be unscrewed from the control box with a wrench. Take the old one to a hardware store to match the size, or order a replacement online using your heater's model number.

When to Call a Professional

If the igniter does not spark at all after several attempts, the igniter battery is likely dead or the igniter itself has failed. Some A.O. Smith models use a replaceable AA or AAA battery in the control box; check your manual to see if yours does. If the battery is not the issue, the igniter module may need replacement, which is a job best left to a technician.

You should also call a professional if you smell gas during or after lighting the pilot, if the main burner will not ignite even though the pilot is burning steadily, or if the pilot light goes out repeatedly even after cleaning the thermocouple. These signs can indicate a gas leak, a faulty gas valve, or a blocked burner, all of which require professional service.

Frequently Asked Questions

How long should I hold the ignition button down?

Hold it for 30 to 60 seconds after the pilot flame appears. This gives the thermocouple time to heat up and signal the gas valve to stay open. If you release too early, the pilot will go out. If it still goes out after 60 seconds, the thermocouple likely needs cleaning or replacement.

What if I don't have a match or lighter?

You can use the electric igniter on the control box instead. Press and hold the ignition button while pointing it toward the pilot opening. The igniter will spark repeatedly. If it sparks but the pilot does not light, try using a match or lighter while pressing the button, since the igniter may be weak.

Is it normal for the pilot flame to be yellow or orange?

A blue pilot flame is ideal, but yellow or orange means the burner is dirty or the air-to-gas ratio is off. The pilot will still work, but you should have the burner cleaned by a professional if the color does not improve after a few days.

What does it mean if the pilot lights but the main burner won't ignite?

The thermocouple is working (since the pilot stays lit), but the main burner may be blocked with debris or the gas valve may not be opening fully. Turn off the heater, wait a few minutes, and try again. If the problem continues, a technician should inspect the burner and gas valve.

Can I light the pilot if I smell a little gas?

No. If you smell gas before lighting the pilot, leave the area when ready, open windows and doors, and call your gas company's emergency number. Do not attempt to light anything. A gas smell can mean a leak, and igniting gas in the presence of a leak is dangerous.