In hot water heaters, an important safety component is the pressure relief valve. If the pressure or the temperature in the heater rises, the valve automatically opens and releases the buildup. The valve does not function correctly, there are high chances of rupture in the tank. If there is leaking water from the relief valve, then this means that there is a fault in the valve and should be changed immediately.
Put a bucket beneath the drain line that is connected to the leaking relief valve. This will contain the leaking water and the water that comes out while removing the valve. Turn off the power of the water heater. If it is an electric heater, then turn off the power at the circuit box and If it is a gas heater, then turn off the supply of gas to the heater.
Then at the bathtub or sink, switch on the water faucet. Allow the hot water to get out for around 15 minutes. This will decrease the temperature and the quantity of water inside the tank. Once the 15 minutes have passed, turn off the faucet of hot water.
On the top of the heater, close the cold water valve. If you are not able to determine that which line is the cold water line, then see at the top of the tank. Almost all the tanks have clearly marked the lines that carry cold and hot water.
Detach the drain pipe from relief that is leaking and then move the pipe counterclockwise with the help of the pipe wrench. This will help you to lose the relief valve. Take out the leaking relief valve from the tank. Then connect the hexagonal nut at the bottom with the pipe wrench. Then again move the valve counterclockwise very carefully. The valve may be a little difficult to be removed at first because of corrosion. If there is a need, then spray penetrating oil on to the valve threads and allow it to soak for around 10 minutes.
Then wrap the threaded portions and the new relief pressure valve with a Teflon tape. The tape will seal the new valve and will stop it from leaking. Then install the new relief valve and turn it inside the tank with your hands. Make sure that the valve is attached to the tank properly or else it will not function the way it should. Once you placed the valve correctly in the tank and is screwed tight, make use of the pipe and to turn the valve tighter. Then attach the drain pipe to the new valve.
Then turn on the supply of cold water at the top of the tank. Also turn on the faucet of hot water at a bathtub or a sink. This will allow the trapped air to get out of the tank or in the hot water line. Let the faucet stay open for some time.
At last switch on the gas or electric supply to the heater and see if the problem has solved or not. if you have followed the above correctly, then there will be no leaking from the relief tap.