The gas control valve is the brain of a gas water heater. It regulates the flow of gas to the burner and pilot, houses the thermostat that senses water temperature, and connects to the thermocouple safety sensor. When this valve fails, you may find the pilot won't stay lit, the burner won't fire, the water is too hot or never hot enough, or you smell gas. Replacing a gas control valve is a more advanced repair than most on this site, and because it involves both gas and a full tank drain, it's important to know exactly what's involved — and when to call a pro.
Warning Signs of a Failing Gas Valve
Common symptoms include a pilot that lights but goes out when you release the control knob (though this is more often a thermocouple), a burner that never ignites even with a good pilot, wildly inconsistent water temperature, a valve body that's visibly corroded or leaking, or the smell of gas around the control. If you ever smell a strong gas odor, stop, leave, and call your gas utility immediately.
A Safety-First Job
Because this repair works directly with the gas supply, many homeowners choose to have a licensed plumber or gas technician handle it. If your gas valve is under warranty, the manufacturer will often supply a replacement — but improper installation can create a serious gas-leak or carbon-monoxide hazard. If you are not fully confident, hire a professional.
Our Top Picks
KAIWEETS Digital Multimeter
Before condemning the gas valve, use a multimeter to rule out the thermocouple and thermostat.
Reliance 100112336 Natural Gas Control Valve
A Resideo-built natural gas control valve compatible with A.O. Smith, Reliance, State, and American branded water heaters — match it to your heater's make and model before ordering.
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How the Replacement Is Done
Step 1 — Shut everything off. Turn the gas control knob to "Off," then close the gas shutoff valve on the supply line feeding the heater. Turn off the cold water supply to the tank.
Step 2 — Drain the tank. The gas valve threads into the tank below the water line, so the tank must be fully drained. Connect a hose to the drain valve, open a hot faucet to admit air, and empty the tank.
Step 3 — Disconnect the gas line and components. Using two wrenches to avoid twisting the pipe, disconnect the gas supply line from the valve. Detach the thermocouple, pilot tube, and burner supply tube (note or photograph how each connects).
Step 4 — Remove the old valve. Unscrew the gas control valve from the tank with a pipe wrench, turning counter-clockwise.
Step 5 — Install the new valve. Wrap the threads with gas-rated thread sealant (not standard Teflon tape unless it's gas-rated), thread the new valve in by hand, and tighten securely. Reconnect the burner tube, pilot tube, and thermocouple in their original positions, then reconnect the gas supply line.
Step 6 — Test for leaks. Refill the tank first (never fire a gas valve on an empty tank). Restore gas, then check every gas connection with a soapy-water solution — bubbles mean a leak. Fix any leak before lighting the pilot.
Step 7 — Relight and verify. Follow the pilot-lighting procedure, set your temperature, and confirm the burner fires and the pilot holds.
Conclusion
Replacing a gas control valve restores a water heater that won't heat, but it's a job that demands respect for the gas supply. Always refill before firing, test every joint for leaks with soapy water, and never ignore a gas smell. When in doubt, this is the repair where calling a licensed professional is the smart, safe choice.