I have two hot water tanks in an 11 unit building One side of the building has water coming out of the hot water spigots and the other side of the building has no water coming out of the hot spigots. There is cold throughout the building. We thought a pipe froze on one side of the building, but with all our efforts we still have no water on the one side. Is there some kind of a shut of valve for the water if the pressure gets to high something of the sort?

temperature check water bout 105F might be element alkali build up inside tank , check thermostat on tank see what temp setting, could be faulty all parts about $ 30.00 on line happy trails

Sounds like you need an expansion tank above your hot water tank. That would help alleviate any pressure that builds up.

The cold water enters the top, but the water is not released into tank at the top. The cold water goes through a "dip tube" This takes the cold water to the bottom of the tank. If you dip tube fails, or breaks, your faucet temperature will slowly drop as you use hot water (vs giving you 60% of tank at full temperature before temperature starts dropping) In normal operation, the cold water is released near bottom of tank, the hot water rises to top, and comes out of the top of the tank.

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Is there water in the hot water tank?.... As in... Is it a new tank?... Tank was filled?... Water come out the drain spigot at the bottom of the two? And the supply v valve... (Bringing for water into two).. Is turned on?
Are the any valves shut off leading away from the tank that never were opened?
Or is it an offer tank that just suddenly stopped
Please tell us more so we can help.

MB

82V52-2 is typical 240Volt 50-gallon electric water heater.
Water heater has to be full of water before turning on power.
This is true for gas and electric water heater.

Once water pipes are connected, you are ready to fill tank.
Turn on cold water shut-off so water enters tank.
Open bathtub spigot on hot side.
When tank is full, water comes out of tub spout full stream.
Let the water run until there is no more air coming out.
Next, open TP lever on water heater for a moment, and this will bleed out last pocket of air.
TP valve is located on upper part of tank, on the side or on top. It is a brass valve with silver-colored lever. Lift lever for a moment and water will exit tank down the overflow tube.
Water heater is full.
Turn on 240Volt circuit breaker going to water heater.

Other links with electric water heater information:
http://waterheatertimer.org/How-to-replace-water-heater-drain-valve.html
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html#cleanelectric
http://waterheatertimer.org/How-it-works.html

You have clog in the water line.
Since all hot water pipes are involved, clog is probably near water heater.

Buy pressure gauge at hardware store that threads onto hose connection.
Brady BTG 100 at Amazon
Picture of gauge

Check outdoor pressure for baseline pressure in your home.
Turn off electricity to hot water heater for an hour or two so there is not scalding water.
Open drain valve on water heater to see if water heater is clogged with sediment.
http://waterheatertimer.org/Water-heater-will-not-drain.html

Put pressure gauge on drain valve and compare with outside pressure.
Open hot water spigot on bathtub and see if tank pressure drops ... if tank pressure drops significantly with bathtub spigot on, then clog is on incoming cold water before tank, and could be on outgoing hot water pipes too.
If tank pressure stays about the same, then clog is on outgoing hot water pipes.

Clog can be sediment caught in cold water shut off valve located above tank. Open and close valve and test pressure again. Take apart incoming cold water pipes above tank and check for sediment. Replace valve. Look at condition of cold water nipple on top of tank.

Sediment caught at hot water elbow near tank.
Sediment can fill up old pipes. Take apart hot water pipes above water heater and see condition.
Look at condition of hot water nipple on top of tank.
You may have to take apart pipes up to first or second elbow.

Pipes can decay at joint where copper pipe connects to galvanized pipe. Check for copper to galvanized connections on cold or hot pipes and replace section of galvanized pipe. Copper pipe will probably be good, the galvanized pipe will deteriorate. Replace copper-to-galvanized joint with 3/4" non-conducting union from hardware store

http://www.waterheaterrescue.com/pages/WHRpages/English/Troubleshooting/Tanklets/backflushing.html
The link above gives a list of reasons for the decreased water pressure at your faucet.

As for draining the tank, it sounds like it's clogged with sediment.
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html

To open a clogged water heater:
Connect a washing-machine-hose to water heater drain valve.
Connect garden-hose to outdoor spigot, and to washing-machine-hose.
Turn on outdoor spigot for 10 seconds and it will open the clogged valve.
http://waterheatertimer.org/Water-heater-will-not-drain.html

'Rheem 81VP15S point of use' is a single-element, 15 gallon, 120V electric.
Other 'point-of-use' sizes range from 2-1/2 to 6 gallon to 20 gallon.

Electric water heaters have 2 parts: thermostat and element. One is not functioning correctly. Most likely the element caused by sediment build-up.

How to determine if tank has element or thermostat problem:
Do not turn off water going into tank. Put hose on drain valve. Open drain valve. Does water come out like open spigot? If water does not flow, then heater is likely clogged with sediment.

Solution 1: If water flows out like a spigot, the thermostat is probably bad. Read: How to replace thermostat.

Solution 2: Water does not flow, so element is surrounded by sediment build-up and cannot heat water. You need to clean out tank with shop vac, and put in new element ... plan full day and 3 trips to hardware store. Simply draining tank will not remove sediment. Sediment is chunky and will not come out voluntarily.

Buy element before starting:
-Turn off electricity
-Open cover on side of tank, remove insulation (these have to be put back for proper operation of thermostat)
-The are 2 electrical parts >>the element and the thermostat which is located above element
-Element wattage is printed on element and also shows on label on side of tank
-I think Rheem element is held in place with 4 hex bolts
-Take photo of element to hardware store so you have part on hand before removing old element
-If element is 1-1/2' diameter hex type, you need inexpensive element wrench from hardware store + the element

Drain tank and clean sediment:
-Read: To open drain on water heater so water comes out
-Read: How to clean sediment out of water heater

There are several possible reasons for this problem. Not knowing your variables as such, I will go thru a couple of the most common reasons.
Most likely, your water heater is older and has lost its efficiency due to lime build up in the tank that settles out of the water that is stored in it. This covers the bottom of the tank where the burner is if it is gas and prevents a good thermal conductivity to the water. As you shower the heater does not recover fast enough to replace the hot water used. The same effect will happen with an electric water heater when the lime build up covers the electric coils that heat the water.
You can try to drain down the tank with the spigot at the bottom of the tank to get some of the lime out, but usually if you do that at this point, it will not remedy the situation enough to make a big difference. If this is the problem, a new water heater will be the way to go.
You can also check the setting on the thermostat and see if it is set too low. 190 F is about the normal setting. If you go much higher, you risk scalding. If your heater is new, it may be set a little low, but not usually so. You can nudge it up for temporary fix for the above lime problem, however you are only prolonging the inevitable of replacing the water heater.
Unless this is a new installation, it is most likely lime build up.
If you have an electric water heater, you may also have one of the two heating elements gone bad. There is one at the top of the tank, and one at the bottom. If they are not both good, the tank will not recover fast enough when you are using it.

if you have build up in the heat exchanger it will cause the unit to use more gas to heat your water, if the gas line isn't sized properly then your going to kick the error codes off. it sounds like you have two problems, first you have build up in your heat exchanger and it needs to be flushed and second you need to get a bigger gas line to it