We have a Rheem 50 gal water heater, model # 81MV52D B. Is there a way to test the heating elements to see if they are working properly?

1) Copy following link for 3-step testing water heater elements.
http://waterheatertimer.org/How-to-test-water-heater-element.html

2) You need $10-15 multimeter from local hardware

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

Copy following two links for illustrated step by step:
http://waterheatertimer.org/How-to-test-water-heater-element.html
http://waterheatertimer.org/How-to-clean-sediment-out-of-electric-water-heater.html

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

Rheem electric water heaters use generic 4500 watt element available at hardware store

Copy following two links for illustrated step by step:
http://waterheatertimer.org/How-to-test-water-heater-element.html
http://waterheatertimer.org/How-to-clean-sediment-out-of-electric-water-heater.html

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

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

Check all wiring at water heater and possible upper thermostat is bad, and in need of replacement.

You will have to run a continuity test on each element. Turn off power to the heater. Remove the cover from each element and with an ohm meter set to ohms 1000 check for continuity on each element where the power is connected. If you have no reading the element needs replacing.

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

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

look for a badly connected power line ont he bottom element, or any connection upstream of the power terminals. voltage readings usually drop to that range when you only have one side of the 220v circuit connected.

one element is off peak and one is boost could be thermostat or ripple controller in fuse box or one dead element