Start a gas water heater by setting the gas control knob to pilot. Press and hold the pilot button while clicking the piezo igniter. Hold the button for 60 seconds after the pilot lights to heat the thermocouple. Release the button and verify the pilot stays lit. Turn the knob to on and set the temperature to 120 degrees Fahrenheit. If the pilot won’t stay lit wait 5 minutes and try again. A failing thermocouple prevents the pilot from staying lit.