In traditional water heaters, gas valves control the pilot light, and in turn, the water temperature. When a water heater turns on, the button on the valve is pressed and a small amount of gas is sent to the pilot head. After the pilot is lit it will heat the thermocouple. The thermocouple will send a small electrical current to the control valve. When the gas valve receives the current, an electromagnet will open a safety valve and allow gas to continue to flow to the pilot.
Water heater gas valves are radiant heaters that work by opening the valve allowing natural gas to flow into the burner where it mixes with oxygen-generating heat. When the water in the tank reaches a specific temperature, the thermostat will shut off the valve. The user also has an option of setting a timer so that once hot water is used, more hot water will automatically be sent to the faucet.