Safety device acts as water heater switch

: My wife started complaining about a lack of hot water, so I ventured out into the garage to check out the water heater. I took the door off and peeked inside and discovered there was no flame. Following the instructions on the tank, I relit the pilot but as soon as I let go of the button, the pilot light went out. I originally thought a breeze may have blown it out, but now I don't know what to do.

A: It sounds like a problem with your thermocouple. It's from the Latin meaning "hot babe with no hot water." Actually, it is a $10 part that is a safety device at the base of your water heater.

The thermocouple acts as a switch. On one end is a part that looks like a thermometer (this part sits in the flame of the pilot). On the other end is a fitting that screws into the gas valve. Connecting the two ends is a wire.

The part works like this: As the one end is heated by the flame, a small electrical charge is generated that tells the gas valve to remain open. When the pilot light goes out, the charge stops and the gas valve closes. This prevents gas from continuing to fill up the base of your water heater.

So this little $10 part does a pretty important job. If the thermocouple is bad, no gas will flow and the pilot will not light.

To change the thermocouple, you will need to disconnect several parts to access it. Before you do anything though, turn off the gas to the unit. Turn the knob on top of the gas valve to the "off" position and turn off the gas supply valve where the gas flex line connects to it. Also, remove the small metal door that stops breezes from entering the burner chamber.

You may get lucky and not have to remove the burner, but chances are you will have to remove it.

There are three lines coming out of the bottom of the water heater's gas valve: the burner's gas line, which is about as thick around as your pinky finger; the pilot light's gas line, which is about one-eighth inch in diameter; and the thermocouple, which looks like a copper wire and is the skinniest line there.

Gently unscrew the three lines from the gas valve and maneuver the burner assembly and thermocouple out of the chamber. The burner may have a tab at the bottom that slips into a slot at the bottom of the water heater. If so, just lift and push it out of the slot.

Some thermocouples just push into the bracket that holds the pilot in place. Others are secured by a threaded fitting. Unscrew the thermocouple fitting at the bracket (or if you're lucky just pull it out). Your new thermocouple will come with several universal fittings for different sizes and methods of connecting it to the bracket.

With the thermocouple in place, maneuver the burner assembly back into place and connect the gas lines and new thermocouple to the gas valve. Turn the gas back on and follow the directions on the tank to relight the pilot.

Your wife will have hot water in about an hour.

Michael D. Klimek is a licensed contractor and president of Pro Handyman Corp. Questions may be sent by e-mail to: questions@pro-handyman.com. Or, mail to: 2301 E. Sunset Road, Box 8053, Las Vegas, NV 89119. His Web address is: www.pro-handyman.com.