A. O. Smith Gas Control Valve: Is It Really Bad?

The Short Answer: The gas control valve on an A. O. Smith tank heater is often blamed for problems caused by the pilot, thermopile, air filter, or flame arrestor. The status light usually settles it. On A. O. Smith’s standing-pilot models, codes for overheating, sensor failure, internal failure, and a valve that will not shut off point to the control itself. Low thermopile voltage does not. Replacement is licensed gas work.

What the gas control does

On a standard A. O. Smith gas tank, the gas control (also called the gas control valve/thermostat) is the box on the front with the temperature knob. It contains the thermostat, the overheat safety (ECO), the valves that feed the pilot and burner, and on newer models a status light. On standing-pilot models it is powered by a thermopile heated by the pilot flame. On Ultra Low NOx models it plugs into an outlet and works with a flue damper and a separate module that monitors the combustion chamber.

Because so much runs through it, a fault anywhere in the system shows up at the control. That does not mean the control is the part that failed.

When the control is likely at fault, and when it is not

A. O. Smith’s service handbook for its standing-pilot FVIR models (opens in a new tab) assigns each status code a check or repair:

Ultra Low NOx models use a longer list. In A. O. Smith’s use and care guide for those models (opens in a new tab), several codes (temperature sensor fault, electronic fault, gas control fault) say to switch the control off and on and replace it if the fault persists. Others point elsewhere: the flue damper, the base-ring air filter and flame arrestor, the igniter and pilot assembly, or a flammable vapor sensor.

Symptoms that usually have a cause outside the control:

• Pilot lights but will not stay lit. A. O. Smith’s checks include a tripped thermal switch, flammable vapors, poor combustion air or draft, a clogged filter or flame arrestor, and thermopile wiring. See why a gas water heater won’t stay lit.
• No gas to the pilot at all. Check the supply valve and whether other gas appliances work. See water heater not getting gas.
• Water on the control. Water usually tracks down from a fitting above. See leaking from the gas control valve.

Symptoms that point to the control and need prompt service:

• The burner or pilot keeps burning with the knob turned to OFF.
• The water is far hotter than the setting, or the relief valve is discharging hot water.
• A gas smell at the control body.

What you can check safely

1. Read the status light for two full cycles and write down the pattern.
2. Relight once following the label on the heater. Standing-pilot controls need a 10-minute wait between attempts, and the light may take up to 90 seconds to start blinking after the pilot lights.
3. Clear the base of the heater. Lint, dust, and stored items around the air openings can choke the burner on flammable-vapor-resistant models. On Ultra Low NOx models, A. O. Smith asks owners to inspect the base-ring air filter at least yearly and vacuum it with the heater off and cooled.
4. Remove flammable liquids such as gasoline, paint, and solvents from the room.

Do not loosen fittings, remove the burner door, or try to swap the control.

What the technician will check

The technician confirms the code, then works through the parts A. O. Smith lists before the control: thermopile output (A. O. Smith’s threshold for replacement is below 350 millivolts), wiring connections, the pilot flame, the thermal switch, and the flame arrestor. If those pass and the control still will not open, hold, or shut off correctly, they replace it with the part listed for your model, then leak-test the connections and check the burner.

Repair or replace the heater?

A gas control is a significant part on an inexpensive heater. If the tank is near the end of its expected life, has rust at the base, or has needed other repairs, replacing the whole heater may be better value. Our water heater age guide helps you read the serial number.

Frequently Asked Questions

Q: My heater shows 2 flashes. Do I need a new gas control? A: Usually not. A. O. Smith lists 2 flashes as low thermopile voltage, which points to the thermopile or its wiring, both much smaller repairs than the control.

Q: Can any universal gas valve replace the A. O. Smith control? A: The replacement must match the model’s gas type, venting, and flammable-vapor-resistant design. Ask the technician to use the replacement part listed for your model number, and to leak-test the connections afterward.