Drain Valve leaking on Hot Water Tank for model #21V40-7

They wear out especially if they are older. You did not say what make and model it is but if there is water coming out the bottom it is time for a new unit. The leak is still happening because even though there is not supply pressure, gravity is pulling the water out the break in the liner.

I recommend safety changes to prevent ruptured water heater and assorted leaks.
135 degree hot water.
Maybe replace TP valve if it is dripping.
Drip pan under water heater with 3/4" drain line to outside.
Expansion tank on incoming cold water line to absorb pressure build-up, and prolong life of tank and plumbing.

Here's why:

1) Yes you can have scalding hot water.

2) I recommend 135 degrees since that will burn the evil right out of ya. And generally kill clothes washing bacteria.
http://waterheatertimer.org/How-to-adjust-water-heater-temperature.html

3) 150 is dangerous and can seriously burn skin in 1.5 seconds. Not safe around children and elderly.

4) Temperature settings on electric water heater are approximate, since thermostats are calibrated approximately, and read temperature through tank wall.

5) Also if you want to increase amount of hot water for high-consumption household, then setting tank temperature upward is one solution since more cold water is mixed with hot, so amount of hot inside tank goes further.

6) High temperature can cause TP valve to release water.
TP valve is pressure-temperature safety valve. Do NOT cap off.
Rating should be 125 psi and 180 degrees ... but all things water heater are approximate, and TP valves need replacement now and then.
It is not recommended by water heater manufactures to use 150 psi TP valve when water heater came with 125 psi. Rating shows in small print on end of TP. New TP valves sold at local hardware. Let tank cool before installing new one.

7) Higher temperature and high pressure can rupture tank.
Pressure over 80 psi shortens life of water heaters and plumbing fixtures. Put BTG100 pressure gauge on water heater drain valve to check pressure.

8) You need a drip pan with 3/4" drain line to outdoors, or to drain vent line, to prevent flood caused by ruptured water heater.
Turn water heater off when going on vacation.
Inspect water heater each 6 months.
Drip pan available at local home center or hardware:
http://waterheatertimer.org/9-ways-to-save-with-water-heater.html#drip

9) Heated water expands and puts pressure on tank and pipes.
Water does not compress... so when water gets hotter it expands against tank wall and against pipes.
Especially in closed system (check valve present) when system is without expansion tank.
Expansion tank is installed on incoming cold water line.
http://waterheatertimer.org/9-ways-to-save-with-water-heater.html#expansion

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Hot water pressure relief valves serve two functions. The first is to remove high-pressure water from the hot water tank. The second function is to act as a high temperature valve to remove water that exceeds a predetermined point for the valve. Both of these relief settings are preset at the valve factory. Many pressure relief valves will come with a metal tag that identifies these release points. If you're attempting to remove the hot water heater pressure relief valve, pay careful attention to ensure that you replace with the correct valve.

Your hot water heater has a pressure relief valve safety mechanism. When pressure inside the water tank exceeds certain limitations, the valve opens up to allow the pressure to be released. A faulty pressure relief valve will not release excess pressure, which could cause extensive damage to your home. You should test the hot water heater pressure relief valve once every six months to ensure proper operation. If the pressure relief valve fails the test, replace the valve with a new one immediately

Locate the pressure relief valve on your hot water heater. The pressure relief valve has a lever handle on top with a drain pipe attached to it. The pressure relief valve is most often on the side of the water tank toward the top. Newer models of hot water heaters have the pressure relief valve on top of the water tank.

Inspect the area around the pressure relief valve for signs of leaking water. If there is leaking water near the relief valve connection, replace the relief valve. If no leaking is evident, proceed with testing the pressure valve.

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Examine the area below the pressure relief valve drain pipe. Most water heater closets either have a drain in the floor below the pipe or the pipe is inserted into another pipe to direct the water out of the home. If the end of your drain pipe is not in another pipe or there is no drain in the floor, place a bucket under the drain pipe to catch water when you test the pressure relief valve.

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Pull the lever handle on the top of the pressure relief valve up with your fingers. A working lever will lift up without difficulty.You should begin to hear water going through the drain pipe. Slowly release the lever to shut off the pressure relief valve. The pressure relief valve is good. If you did not hear water running through the drain pipe, lower the lever on the pressure relief valve and replace the valve. If the lever is difficult to raise, do not force the lever. Replace the pressure relief valve.

Now with all that said if you have a closed loop water supply system and you have a pressure vessal/expantion tank it may have gone bad and is making the TP valve leak. you can call your water provider to see if you have closed loop system.

When you say drain valve, do you mean TP valve?
Two different things: -drain valve and -TP valve

-Drain valve is located near bottom of tank and has hose thread on end.
-TP valve is brass and is located on side of tank tank near top on , and has a pipe that runs down within 6" of floor, or pipe goes into a drain pipe. DO NOT CAP OFF TP VALVE because this is safety outlet that prevents extremely hot water from rupturing tank.
http://waterheatertimer.org/Leaking-water-heater.html

1) If drain valve located near bottom of tank is leaking, it can be capped with a garden hose cap from hardware store-home center. Thread cap on end of drain valve.

2) If TP valve is leaking.
a)Turn down thermostats on water heater
http://waterheatertimer.org/How-to-adjust-water-heater-temperature.html
b)Replace TP valve
http://waterheatertimer.org/How-to-replace-TP-valve.html
c) Install expansion tank on incoming cold water line
Buy expansion tank at hardware-home center-plumbing supply and tee straight out from cold water line and attach expansion tank. About the size of small football.
http://waterheatertimer.org/images/Expansion-Tank-1-82.jpg


4) Mythbusters blows up a water heater for your enjoyment U-tube
Video shows that extraordinary pressure is needed to blow up heater.
This event has only been reported once in past 10 years that I have read, and it blew out side of home. Stats for this type event don't exist in insurance company records, so you are safe - just don't cap off TP valve.

5) Add a comment for more free help.
Also take advantage of fixya phone service.
For a price, expert speaks with you over phone while you work on heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

You can try to crack it open and get a little piece of crud out of there, I'm sure that is all it is, Just get a tray or something to catch the water, It should stop it, If it gets worse, turn the water off to the heater, then open the valve and hope the bigger piece of crud comes out. It is about all you can do, other than drain the whole thing and take the valve apart and replace the rubber in it. Check it out, Hope this helps.

12 year old water heater is getting near the end.
Some tanks last 20 years, but that's the exception.
To find exact age of your brand water heater:
http://waterheatertimer.org/pdf/WaterHeaterSerialNumberDecoder.pdf

Leaking TP valve:
1) Lift TP lever and gently lower back into position to see if that stops leak.
Occasionally something gets stuck in the valve.
2) Sometimes water heater temperature gets turned up because heater is not producing as much hot water as before, and higher temps cause TP to release pressure because of overheating.
Dial temperature down to 120 degrees.
http://waterheatertimer.org/How-to-adjust-water-heater-temperature.html

3) If steps above don't fix problem, replace TP valve >> TP valves have 125 or 150 degrees rating >>> older tank shouldn't be running above 125 because higher temps cause more pressure on tank, so thermostat should be lower than 125 degrees TP rating.
Buy replacement TP at any hardware store + a roll of teflon tape to seal pipe threads.
Turn gas control to pilot ... this will keep pilot lit but burner will not fire.
Let water cool, and then drain some water out of tank.
If TP valve is on side of tank, then open drain on side of tank and drain water until it is lower than valve level. Open bathtub spigot to let air into line.
http://waterheatertimer.org/Water-heater-will-not-drain.html
Be careful around water that is higher than 120 degrees F >> you can get burned quickly >> apply cold water to any burn.
Use pipe wrench and unscrew TP valve counterclock-wise.
Install new TP and put teflon tape on threads.
Re-fill tank completely and open tub valve on hot side until water is running >> then turn gas control back to original position.
Do not fire up any water heater before tank is completely full of water or this could damage tank.

To read more preventative information about water heater leaks and age problems:
http://waterheatertimer.org/Water-at-bottom-of-water-heater.html

It sounds like two problems.
Problem 1) Clog inside faucet or clog inside pipes at faucet
Remove supply tubes leading to faucet and see if problem is inside pipes or inside faucet.
My bet is clog inside faucet.

If you have galvanized pipe that meets copper pipe, this can be trouble spot.
Article on clogged water pipes at Inspectapedia:
http://www.inspectapedia.com/water/Water_Pipe_Clog_Repair_Guide.htm

Article on clogged pipes:
http://www.waterheaterrescue.com/pages/WHRpages/English/Troubleshooting/Tanklets/backflushing.html

Problem 2) Water heater leak ... you say tank valve is leaking? Is that cold-water shut-off valve? Or tank drain valve? Or TP valve?

If cold water shut-off is leaking, then replace shut off.

If tank drain valve is leaking, then check if plastic valve is cracked. If drain valve is cracked, then replace with a brass valve from Home Depot. If plastic valve breaks off, then use hammer and screwdriver to gently chip out the broken plastic valve. New valve threads need teflon tape to seal pipe. If valve is just dripping, then put garden-hose cap over end of valve and screw down tight.

If TP valve is leaking, then replace with same temperature and pressure rating. New TP valve threads need teflon tape to seal pipe.

Problem 3) If pressure is low all over house:
Buy pressure gauge at hardware store that screws onto hose connection.

Test pressure on outdoor spigot.
Open faucet and check if pressure drops. This says if problem is inside pipes that enter house.

Test pressure on water heater drain valve.
This says if pressure problem is before -or- after water heater.

If problem is before the water heater, then shut-off valve located on cold water line is suspect.
If problem is after water heater, it could be in hot water outflow pipe on top of water heater, or a nearby elbow.
Remove hot water line leading from water heater and check pressure. This says if problem is where hot water leaves tank.
Read articles above about clogs inside water lines.

If you are reffering to the drain valve at the bottom of the hot water tank. It may be leaking due to the O ring being cracked or worn out. You can either drain the tank and replace the valve or you can buy a hosebib brass cap and thread it on the existing valve. There is no cause for alarm when doing this as this valve is just to drain the tank when replacing your hot water heater

If you're sure it's the DRAIN, just get a garden hose cap for it (your other option is to replace the valve - drain tank, replace valve, refill).
NEVER CAP THE RELIEF VALVE DRAIN!

drain valve must have already been leaking, that's why someone put the cap on. It's ok to cap the drain but never the pressure/temp relief. If the water is coming out of the drain (not around it) you could either replace the cap or the drain valve to stop the leak - otherwise it's time for a new water heater.