The Pilot Light on My Water Heater Won't Stay Lit

Check the shut-off valve located on the main gas line coming into the hot water heater. Make sure the valve is turned completely to the "On" position. If gas is not flowing properly to the pilot light, it could go out. Take a look at the orifice where the pilot light is emitted. Look for dirt or debris that may be blocking flow.

Turn off the power to the hot water heater and shut off the pilot light, if it's lit, by turning the gas shut-off valve to "Off."

Set the dial on the multitester (also known as a multimeter) to check resistance and at the lowest ohm scale available. Touch one probe to each thermocouple terminal and look for a resistance reading. A zero or a nearly zero reading means the thermocouple is good. A higher reading indicates a broken thermocouple.

Set the multitester to read voltage and at the lowest voltage setting available. Again, put a probe on each thermocouple terminal, and then touch the end of the thermocouple with your finger. Your body heat should be just enough for the thermocouple, a transducer, to convert the heat energy of your body to an electrical impulse that will register on the multitester. If it doesn't create this electrical impulse, the thermocouple is bad.

Make sure the gas shut-off valve is still off and turn the water heater's temperature control to "Off" as well.

Loosen the nuts that hold the thermocouple in place near the bottom of the gas control valve, which is located at the front of the water heater. Use a pair of open-end wrenches to loosen the nuts. Before snapping the thermocouple loose from the end where the pilot light should be located, note how it's held in place. The replacement thermocouple will need to be installed the same way, and each manufacturer has a different means of attachment.

Remove the old thermocouple and replace it. Make sure your new thermocouple is the same length as the old one. Thermocouples may be purchased at home centers and hardware stores.

Snug the locking nut that holds the thermocouple in place on the gas control valve by hand-tightening it until firm. Finish tightening gently with an open-end wrench. Be sure not to over-tighten the nut.

Open the gas shut-off valve and relight the pilot light, making certain to follow the instructions printed on the hot water heater. Usually, you will need to set the gas control valve to "Pilot," ignite the pilot light with a match or lighter and hold the valve down for a few seconds to warm the thermocouple. Next, slowly move the valve to the "On" position. Turn the temperature control back up until the burners ignite.

Check to see that the pilot light remains lit. If it continues to go out, the gas control valve unit itself may be malfunctioning by sending out low pressure or by shutting off inappropriately. Call a service repair person to replace the valve.