There are safety issues to keep in mind when changing a water heater gas valve. Changing the valve can be a dangerous task because it involves working with flammable, poisonous gas and extremely hot water temperatures. Be sure to have all the necessary information and tools handy before beginning this task, as it is better to be safe than sorry.
If the tank has a pilot light, make sure it is off. If it has an electric igniter, flip the power switch off. Once the power and gas supply to the tank is cut, give the water heater a chance to cool down before touching the parts. Again, safety is the main concern. Wearing heat safety gloves might be handy, but they will need to be very thin in order to maneuver the small parts of the tank.
Inspect the tank and any hoses, valves, joints or copper lines to make sure there are no punctures, pinches or cracks. There should be no pure oxygen anywhere in the vicinity. Also refrain from smoking while doing this job, or creating any sparks or fire around the gas tank. These things could cause an explosion. Just like the instructions say on an aerosol can of hair spray, keep any sharp objects that could puncture the gas tank away from it, as well as open flames.
2. Turn Off and Drain the Water
Turn off the water supply to the tank. There should be a shut-off valve near the tank itself. Generally, right-is-tight and left-is-loose just like turning a screw, and so turning the valve clockwise should close off the valve and restrict the water flow. If this valve is not working properly, go ahead and shut off the main water source to the residence.
Most people now take the extra precaution of draining the remaining water from the heater. If the water flow is not halted completely, scalding hot water could spray or drip out of open valves and cause terrible burns. Secure a hose to the tank drain pipe, and run it to a sink, tub, or even outside, where several gallons of hot, potentially rusty water will not cause damage. Having a few old towels around can be helpful, to catch any drips from the hose connection.
3. Watch for Leaks
After replacing and tightening the gas valve, turn the water supply back on first, and when the tank is full, turn the igniter switch back on or carefully light the pilot light. Watch for leaks throughout the tank. This could lead to major future problems, including flooding, fire, or gas poisoning. If you find any leaks, tighten the component around it. Properly fitting parts help to get the most life out of the tank and increases safety. There are many kinds of plumber's tools that may help, from special tapes to adhesives and wrenches. If the leak cannot be made secure, the part may need to be replaced, or you may need to call a plumbing or gas expert.