Starting Your A.O. Smith Water Heater: The Basic Steps
To turn on an A.O. Smith water heater, you locate the gas control valve (usually a black or brass knob on the front of the tank), set it to the pilot position, hold down the ignition button while lighting the pilot with a long lighter or match, then move the valve to the on position once the pilot stays lit. The whole process takes about five minutes if the pilot catches on the first try.
Most A.O. Smith water heaters use a standing pilot system, which means a small flame burns continuously to ignite the main burner when you need hot water. Some newer models have an electronic ignition instead, which skips the manual lighting step entirely. If you have an electronic model, you straightforward turn the valve to on and press the ignition button—the system lights itself.
Key Takeaways
- The gas control valve has three positions: pilot, on, and off—you move through them in order when starting the heater.
- The ignition button sits next to the valve and must be held down while you light the pilot with an external flame source.
- Once the pilot flame is visible and steady, release the button and turn the valve to on within 30 to 60 seconds.
- If the pilot does not stay lit after you release the button, wait five minutes before trying again—the thermocouple needs time to cool.
- Electronic ignition models light automatically and do not require a match or lighter.
Locating the Gas Control Valve and Ignition Button
The gas control valve is mounted on the front or side of the water heater tank, usually near the bottom. On A.O. Smith units, it is typically a round knob with three labeled positions: pilot, on, and off. The positions are marked either with words or with symbols—a small flame for pilot, a larger flame for on, and a line for off.
Next to the valve, you will see a small red or black button labeled "ignition" or "spark." This button triggers the spark that lights the pilot. Some A.O. Smith models have the button recessed slightly into the valve body, so you may need to press it firmly. Keep a long lighter or long-handled match nearby before you start—you will need an open flame to light the pilot manually.
Setting the Valve to Pilot and Lighting the Flame
Turn the gas control valve counterclockwise from the off position to the pilot position. You should hear a soft click as it locks into place. Do not force it—the valve will stop when it reaches the correct position.
Hold the ignition button down with one hand while you bring the flame to the small opening at the base of the pilot tube with the other. The pilot tube is a thin metal line running from the valve down toward the burner assembly. You should see a small blue flame appear within a few seconds. Keep the button pressed for another 10 to 15 seconds after the flame appears to may support the thermocouple (a safety sensor) heats up enough to hold the flame steady.
If the pilot does not light on the first try, release the button, wait about five minutes, and try again. The gas needs time to clear from the chamber, and the thermocouple needs to cool before the next attempt.
Moving the Valve to On and Confirming the Burner Ignites
Once the pilot flame is burning steadily and you have held the button for 15 seconds, release the ignition button. The pilot should stay lit on its own. If it goes out when ready, the thermocouple is not hot enough yet—wait a few minutes and repeat the process.
When the pilot is holding steady, turn the gas control valve clockwise from pilot to on. You should hear the main burner ignite with a soft whoosh sound, and you will see a larger flame appear in the burner assembly below the pilot. The water heater is now running and will heat water on demand.
If the main burner does not ignite after you turn the valve to on, turn it back to off, wait a minute, and try the process again. Sometimes the pilot needs a moment to build enough heat to trigger the main burner's ignition sensor.
Troubleshooting When the Pilot Will Not Stay Lit
If the pilot lights but goes out as soon as you release the ignition button, the thermocouple is likely dirty or failing. The thermocouple is a thin metal rod that sits in the pilot flame and generates a small electrical signal that tells the valve to stay open. When it is covered in dust or corrosion, it cannot generate enough signal to hold the valve open.
To clean the thermocouple, turn the valve to off and let the heater cool for 10 minutes. Locate the thermocouple—it is the thin rod sticking into the pilot flame area. Use a soft brass brush or fine steel wool to gently scrub the tip of the rod, then try lighting the pilot again. If cleaning does not work, the thermocouple may need replacement, which is a job for a licensed technician.
If the pilot lights and holds but the main burner will not ignite when you turn the valve to on, the issue is usually a blocked burner orifice or a faulty ignition sensor. These problems also require professional service, as they involve gas line work or electrical components.
Electronic Ignition Models: A Simpler Process
Some newer A.O. Smith water heaters use electronic ignition instead of a standing pilot. These models have a battery-powered spark generator that lights the burner automatically when you turn the valve to on. You do not need a match or lighter.
To start an electronic ignition model, straightforward turn the gas control valve from off to on. The ignition button will spark automatically, and the burner will light. If the burner does not ignite within a few seconds, turn the valve back to off, wait a minute, and try again. If it still does not light, check that the battery in the ignition module is fresh—most A.O. Smith electronic models use a standard AA or 9-volt battery that you can replace yourself.
When to Call a Professional Technician
If the pilot lights and holds but the main burner will not ignite, or if the pilot will not light no matter how many times you try, the problem is beyond a straightforward restart. A blocked gas line, a faulty valve, a broken thermocouple, or a failed ignition sensor all require a licensed technician to diagnose and repair safely.
Do not attempt to disassemble the gas valve or burner assembly yourself. Gas water heaters operate under pressure, and improper reassembly can create a gas leak or fire hazard. If your A.O. Smith heater will not turn on after following these steps, contact a local plumber or the manufacturer's service line for guidance.
Frequently Asked Questions
How long does it take for hot water to arrive after I turn on the heater?
Once the main burner ignites, the heater begins warming the water inside the tank. You will have hot water at your tap within 10 to 15 minutes, depending on how much cold water is in the pipes between the heater and your faucet. The first water out will be cool as it flushes the cold water ahead of it.
What if I smell gas when I light the pilot?
A faint gas smell during the first few seconds of lighting is normal—you are burning off residual gas in the chamber. If the smell persists after the burner has been running for a minute, or if you smell gas anywhere else near the heater, turn the valve to off when ready and leave the area. Do not use any electrical switches or open flames. Call your gas company's emergency line from outside the house.
Can I turn off the heater by just turning the valve to off?
Yes. Turning the gas control valve to the off position stops the flow of gas and shuts down both the pilot and the main burner. The heater will cool down over the next few hours. You do not need to do anything else to safely turn it off.
Why does the ignition button need to be held down?
Holding the button keeps the gas valve open while the thermocouple heats up. Once the thermocouple is hot enough, it generates a signal that tells the valve to stay open on its own, so you can release the button. If you release it too early, the valve closes and the pilot goes out.
Is it normal for the pilot flame to be blue?
Yes. A blue pilot flame indicates complete combustion and proper gas flow. A yellow or orange flame suggests incomplete combustion, often caused by dust in the burner or a problem with the gas supply. If the flame is not blue, have a technician inspect the burner and gas line.