1. Check the status of the pressure relief valve if there is little or no water in it and then look at the surrounding floor of your water heater. If there is saturation of water on the floor, then there is no water in the tank and the overflow has blown. If this is the case, you should turn off your water heater immediately by flipping the breaker to the off position or turning the actual gas valve off. In this type of problem, the valve will need to be discarded, and there are certain cases where similar had to be done with your heater.
2. Check the overflow for leaks around its threads where it is screwed into the heater, and if there is a leak, you will need to re-coat the threads using a plumber’s pipe compound. First, you have to turn the heater off and then release the pressure inside by pulling the handle up on the valve. Afterward, place a pipe wrench on the extension tube that leads from the valve and then unscrew it. After unscrewing, you can then coat the threads with the pipe compound and rethread the valve in, tightening it in a firm but gentle manner. Then, reattach the extension tube.
3. Try to see if the leak from the overflow is the main seal or if a piece of dirt has compromised the seal. Turn off your heater and then open and close the valve several times, where you will see that water will splash from the overflow tube and onto the floor, which is why you need to put a bucket underneath. Flush water through the valve to free any particle that may have lodged itself beneath the seal, which might have caused the leak. Turn the heater back on and wait for 2 days to see if the valve reseals itself. If not, then you have to replace it.
Replacing the Overflow
1. Turn off the gas to your water heater or flip the breaker if you are having the electric type. Then, close the cold water cut-off valve that goes into the heater.
2. Open the overflow at the bottom for about 60 seconds to drain the water out of the tank and relieve the pressure. Then, remove the overflow pipe from the valve, which may have been soldered or glued in place, so you might have to cut it off.
3. Using a pipe wrench, unscrew the old valve and replace it with the new one by screwing it in until tight. Reattach the valve drain pipe with Teflon tape on its threads. Open the cold water cut-off and then check for leaks around the overflow.
There you have it. You have fixed the leak from your hot water heater overflow!