Water Heater Relief Valve page

How to troubleshoot Electric Water Heaters. Water heater relief valves leak for 4 reasons. Please read this first: Relief valve warning 1 The valve is old and it starts to leak, They can just start to leak in less then a year so if it is a few years old, that may be all there is to is so it just needs to be replaced.  Pictures and instructions will follow. 2 The water is too hot. water heater relief valves will blow at 210 % f but most of the time the relief valve will blow before that temperature because of the extra pressure caused by the water expanding. This in not to be confused with normal thermo expansion. This is the water heater over heating and is very dangerous. if you have noticed the hot water spitting out of the spout or the water being very hot almost like steam you have a bad control and should shut your water heater off  and have the problem fixed. In this example the relief valve is doing it's job, but may need to be replaced after the control problem is fixed. 3 the pressure is too high relief valves are set at 150 psi. if the pressure coming into your house is 150 psi or more the relief valve will never stop leaking, Now just because your relief valve will not stop leaking does not mean your pressure is 150 psi it may just be bad. 4 Thermo expansion  When water heats it expands in most cases with a standard 50 gallon 50,000 btu gas water heater with house pressure of about 50 psi it will not expand enough to be a problem. but with higher recoveries and  or higher house pressure, a domestic water expansion tank may be needed to absorb the expansion of the water. Now that you know what may be the cause. You need to understand that it can be dangerous to mess with a relief valve. You can be scalded or create a very dangerous situation, possibly resulting in death. It is better to have a pro do it for you.   Ok so you want to replace your relief valve. First turn off the power if electric. and turn gas to pilot setting. Then turn off the water to the tank. then open a faucet at a lower level then the water heater if possible. If the water stops running you are ready to replace the relief valve if not you may have a bad mixing valve, So you will have to turn off your main water valve and drain the water out of the lines at a sink or something. It is not necessary to drain the whole tank just drain it to below the relief valve.

First I Like to prepare the new one you can use tape or pipe dope     Then you have to remove the dip tube (make sure you put this back) I just un soldered it but you can cut it and put it back together with a 3/4" compression coupling. Then remove the other piece of pipe that screws into the relief valve. This is a good time to stop and make sure the water is off. and that the sink you have the faucet on in is still on and there is no water running (a slow drip is not a problem) Now put a wrench on the top of the relief valve and turn counter clock wise as in the picture. Take the old one out and put the new one in and tighten, make sure it is tight. then put the other parts back you are done Make sure the water is on and the tank is full and water is flowing good out of any hot water faucet before you turn the power back on. Note for residential water heaters A watts XL100 is good but check your  Btu's to be sure. Some water heaters have thick insulation and you may need one with a linger shank.