Hello, I have a Rheem 81V52D 50 gal. residential water heater. I had the upper element short out. I replaced both the upper & lower elements with the 4500 watt 230v. My problem now is that the upper circuit breaker keeps tripping about every hour. The water gets hot as long as I keep re-setting the breaker on the thermostat. Do you think that I may have a bad thermostat?

1) Copy following links for standard wiring that applies to all brands electric water heater: wire colors vary, and do not matter.
You probably have ordinary residential non-simultaneous water heater.
http://waterheatertimer.org/How-to-wire-water-heater-thermostats.html
http://waterheatertimer.org/images/WH-w-combined2-1000.jpg

2) Look at tank label.
Typical label will show number of elements (upper and lower)
And give wattage for each element.
http://waterheatertimer.org/Figure-Volts-Amps-Watts-for-water-heater.html#label
http://waterheatertimer.org/images/Whirlpool-energy-smart-watt-rating-IMG_2600.jpg
Notice also total connected watts.
If total connected watts is same as individual upper or lower element watts, then you have ordinary residential non-simultaneous tank.

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

Replace heating elements can be found at amazon, click here and take a look: Amazon com rheem heating element . I hope this was helpful... cheers

If your top element is bad the the lower element will never turn on be cause the top element completes the 240 circuit. It is like a resister in a circuit. Make sure top element measures out at 13 ohms.

Copy following link for step-by-step
http://waterheatertimer.org/How-to-replace-water-heater-element.html

You might want to test them first.
If water heater has some hot water, then upper element is good.
http://waterheatertimer.org/How-to-test-water-heater-element.html

If elements test good, then problem can be thermostats.
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

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

It could be element shorted to ground through steel tank, so don't touch tank when breaker is ON.
Or you have undersized 12 gauge wire and 20 amp breaker and the heat has loosened breaker on the busbar. Breaker trips when heat exceeds breaker limit. Jiggle breaker and listen for crackling sound.

To restore hot water now:
Turn off circuit breaker, and open top cover then Push in reset button on top of heater to restore functionality. Put back insulation and factory cover.
To fix water heater: test and replace bad element.
http://waterheatertimer.org/How-to-test-water-heater-element.html
If problems continue
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html#trip-breaker
http://waterheatertimer.org/Troubleshoot-household-electricity.html

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

The first thing I would do is to turn the thermostat up and down several times,wait a few mins. and do it again. Then run hot water until element comes on. Let it run for a few mins and then turn it back to lowest setting.
I never really came up with a good reason why this works some times but I always tried to save money for my customers and quite often I was 30 or more miles to supply house and it was a cheap fix.
I think you probably will end up replaceing thermostat like your thinking so good luck. Thank you.

You have electric water heater.
Electric water heaters are fully repairable by homeowner, excluding hybrid type.

Rheem electric water heaters:
http://www.rheem.com/products/tank_water_heaters/electric_water_heaters/
Rheem fury series manuals and models
http://www.rheem.com/product.aspx?id=09DF2BDD-5E11-4D32-B574-84ACFB8A4619

Age of Rheem water heater is first 4 digits of serial number located on side of tank: for example 0705 means July 2005.
Serial number also shows model number & wattage of elements.

A) If your water heater receives very cold incoming water, it may not heat fast enough to keep tank warm.
Add a tempering tank.
http://waterheatertimer.org/Tempering-tank.html
Add insulation over entire water heater except TP valve. Insulate pipes completely.
Read more information:
http://waterheatertimer.org/9-ways-to-save-with-water-heater.html

B) If cold outside temperatures are not to blame, your water heater may have a bad thermostat or bad lower element.

C) 40 or 50 gallon water heater is 240Volts and tank will have 2 access panels on front.
Rheem ships all water heaters with 4500 Watt elements.

Narrow down the suspects:
D) Water heater has some hot water.
This tells us upper element is working.
And that water heater electricity is working.
And that reset button is not tripped.
And that heater is not experiencing run-away overheating event.

That gives us 3 solid suspects.
1) lower element is burned out. Test lower element using inexpensive multi-meter from Home Depot.
http://waterheatertimer.org/How-to-test-water-heater-element.html
Replace element with same wattage shown on label, and clean out sediment:
This will restore water heater to full 99% efficiency.
http://waterheatertimer.org/How-to-clean-sediment-out-of-electric-water-heater.html
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html

2) Upper or lower thermostat is bad. Replace both thermostats for about $25.
http://waterheatertimer.org/How-to-replace-thermostat-on-electric-water-heater.html
If you want to test thermostats and all parts before replacing anything:
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

3) Burned or shorted wire. Turn off power. Open covers on side of tank. Remove insulation. Inspect parts for signs of high heat and burning. Especially lower element. Tighten any loose wires. Replace part that shows signs of burning.
Put insulation and cover back over thermostats so cooler outside temperature doesn't cause thermostat to misread tank temperature.
Rheem element

You can open the top up again. I would not turn the temp higher than 130 degrees, maximum. However, there should be above the thermostat a red button. This is where the power wires connect to the thermostats and heating elements. Sometimes this button needs to be reset, press it and discern if you hear a click sound. This means that the high temperature safety switch has tripped open and you had to manually "reset" it. There are two thermostats by the way. The water heater usually works this way. There are two thermostats and two heaters. The upper tank heater turns on first and it heats the top half of the tank. Then when the thermostat above is satisfied it then allows the bottom heater to come on and heat the bottom half of the tank. You might want to set the bottom heater thermostat as well. This is made this way because it is actually faster and more efficient to heat the top half first and the bottom half secondly. Try this first with the reset button. We could check voltages, but that requires a level of knowledge and safety that I am not sure that you are comfortable with. Pictures of the upper and lower thermostats and connections will help if the "reset" does not do the trick. By the way, not meaning or implying anything, but did you move the thermostat in the right direction? Sometimes the dials can be confusing.

Lower element can be burned out and still read 230V across screws

1) We know thermostats are working because elements test 230V.
2) We know upper element is working because tank has some hot water.
If upper element is burned out, tank will have no hot water.
http://waterheatertimer.org/How-it-works.html

3) Here's how to test lower element:
http://waterheatertimer.org/How-to-test-water-heater-element.html

4)Here's how to replace element
Rheem element is 4500Watt bolt-in type
http://waterheatertimer.org/How-to-clean-sediment-out-of-electric-water-heater.html

5) Rheem manual says: Heaters furnished with standard 240 volt AC, single phase non-simultaneous wiring, and 4500 watt upper and lower heating elements.
http://waterheatertimer.org/pdf/Rheem-spec-sheet.pdf

Rheem 4500Watt element

yes bottom 1 bad