Few things in life are more frustrating than to wake up bleary-eyed on a cold morning ready to take a nice hot shower only to discover that all that comes out is a steady stream of ice water, followed, of course, by a steady stream of expletives from you.
Most likely, the water heater pilot light has gone out. But don't feel too defeated. You do not have to take a cold shower nor do you have to wait for the gas company to come out. You can safely re-light the pilot flame and have hot water again in less than 20 minutes.
Locate the hot water heater in advance. If you are not sure where the hot water heater is in your house or apartment, take a few minutes to find it before you have a problem.
In older homes it is usually in the basement. In newer construction it will be in a closet inside or outside the house, or in a steel enclosure attached to the outside of the structure.
Turn the control knob to "off." All residential gas water heaters have a control valve at the bottom of the tank with a small control knob labeled "on," "off" and "pilot." Turn the knob to "off."
Note: It is not necessary to turn off the gas supply line to the water heater, only the control knob on the tank.
Remove the access panels. The water heater pilot burner is located under the tank. To get to it, remove the large outer cover panel at the bottom of the tank under the valve. Lift up to remove it. Behind this panel will be a smaller access panel that is removed by sliding it left or right while pulling on it.
Locate the pilot burner. Looking through the access openings, follow the one-quarter-inch aluminum tubing leading from the control valve to where it terminates under the tank. The fitting at the end is the pilot burner.
Turn the control knob to "pilot." If the control knob has been in the "off" setting for at least four or five minutes, turn it to the "pilot" position.
Light the pilot flame. Strike a long fireplace match or better yet, use an extended lighter (such as Scripto "Aim-n-Flame") and hold the flame right next to the pilot burner. Now push down hard on the control knob or on the red knob if there is one. You will hear a slight hiss as the gas makes its way to the burner.
Look through the access holes to the burner. A blue flame should appear within five seconds. Continue holding down the control knob for one minute after the flame is lit, then turn the knob to the "on" position. You will hear a "whoosh" as the main burner is ignited.
Replace the access panels. Take care to re-attach the access panels properly as they act both a safety shield against flare-ups and a wind shield to prevent future loss of the pilot flame.
Now pat yourself on the back for having saved yourself the punishment of a cold shower and the inconvenience of waiting for help. In about 15 minutes that hot shower you have been looking forward to will be ready.
Incidentally, if you have the problem of running out of hot water too soon, you may be able to extend the hot water supply by increasing the water temperature. Turn the large dial on the front of the control valve clockwise in one-quarter-inch increments. For safety reasons though, do not exceed 145F.
And finally, keep in mind that these pilot lighting instructions also apply to gas-fired furnaces. You will find a similar gas control valve behind the large sheet-metal access panel on the front or bottom of the unit.