Directions are unclear. What does tab at the top mean? Do I cut away all the insulation at the electric hot water heater thermostat? (directions say "side seam over thermostat" What does that mean?

Guessing that you have 240Volt residential non-simultaneous electric water heater? And that you have 30 amp breaker and 10 gauge wire. And that water heater is located within 100 feet of breaker box. And there are no leaks running hot water out of tank. And that you installed fully brand NEW elements of same wattage as old elements. And that fully brand new thermostats were installed, and wiring exactly duplicates wiring that was present before. And that factory-insulation was re-installed over elements and thermostats.

1) Guessing the 'hot water shut off' means the ECO red reset button located on upper thermostat keeps tripping and cutting off electric power to water heater?
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html
http://waterheatertimer.org/images/WH-w-combined2-1000.jpg
http://waterheatertimer.org/How-to-test-water-heater-wires.html

2) If the ECO is tripping, then water is getting too hot, or there is shorted wire located near the upper thermostat, .
Typically replacing both thermostats and replacing elements will solve this problem .... assuming that new thermostats and elements are good, and wiring correct.
Double-Check your wiring on upper and lower thermostats.
Test wires for short.
Make sure factory-insulation is re-installed over thermostats so cool room temperature will not affect temperature reading.
Check that thermostats sit flat against steel tank.
Many short draws hot water can also cause stacking event that will trip circuit breaker.

3) Add comment and say what you find using checklist above.
Be careful to explain findings fully, using same words found on links above, so illuminated diagnosis can be made.

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

1) Make sure factory-supplied insulation and cover are reinstalled over thermostats, or cooler room temperature causes thermostat to under-approximate tank temperature, and this causes overly hot water.
http://waterheatertimer.org/images/Tank-with-insulation-2-600.jpg
2) Replace both thermostats.
Sticking thermostat can seem to act normally when tested, but when left alone it sticks, causing runaway overheating.
http://waterheatertimer.org/How-to-replace-thermostat-on-electric-water-heater.html

More resources:
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

Ordinary tank-type electric water heaters are fully repairable by homeowner.

A) Basic info on Rheem
Rheem electric water heater website:
http://www.rheem.com/products/tank_water_heaters/electric_water_heaters/
Find age of Rheem: look 2nd and 3rd digit of serial number, for example 06 is 2006

B) Water heater has some hot water.
That says certain things: upper element is working, water heater electricity is working, reset button is not tripped, and heater is not experiencing run-away overheating event.
http://waterheatertimer.org/How-it-works.html

C) That leaves 4 suspects that cause lower amount of hot water.

1) TP valve is running hot water out of tank -or- leaking faucet is running hot water out of tank.
Check for leaks
http://waterheatertimer.org/How-to-replace-TP-valve.html

2) 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:
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

3) Burned or shorted wire located between upper and lower sections of tank.
Turn off power. Open covers on side of tank. Remove insulation. Inspect parts for signs of high heat and burning. Especially check 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.
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

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 water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

There should be a short **** in the insulation. Carefully seperate insulation to access elements thermostat and reset. It's always possible that the insulation shifted position during manufacture so you can use a utility knife to make a small opening thru insulation if you need to. If you do this I would suggest that you shut power off to your water heater before cutting insulation just to be on the safe side. I hope this helps you. Thanks.

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 shown 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 in case you need to buy new generic 4-bolt type 4500 Watt element from hardware store.

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) 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:
C) 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 4500 watt element

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 have electric water heater.
Electric water heaters are fully repairable by homeowner.

Reliance is AO Smith company
http://www.aosmith.com/OperatingUnits/Detail.aspx?id=138&ekmensel=c580fa7b_12_0_138_3
http://www.reliancewaterheaters.com/prod/elec.html

Age of Reliance water heater is shown on serial number located on side of tank: first digit is letter. Next two digits are numbers: for example C06 means 2006.
Serial number also shows model number & wattage of elements in case you need new element from hardware store.

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 element.
Narrow down the suspects:

Water heater is 240Volts since you have more than 1 thermostat.
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.

Gas or electric?

1) Electric heater can be completely covered with insulation except TP valve. Set electric heater on insulated surface. Insulate pipes completely right down to tank.

2) Gas heater is different.
No insulation over combustion area, or gas valve, or air inlet or. No insulation on top of tank that will interfere with venting of dangerous combustion products including odorless CO gas. Foam insulation on pipes should stop 10" short of tank top. No insulation within 6" of the 3-4" inch galvanized vent pipe.

Here's photo with gas water heater insulation tips:
http://waterheatertimer.org/images/Insulate-gas-water-heater.jpg
http://waterheatertimer.org/9-ways-to-save-with-water-heater.html

3) Tankless gas. No insulation on box. No pipe insulation within 12". No insulation near vent pipe.

4) How much clearance between heater and chimney?? Not sure what that means. Is that the water heater vent stack? Or where vent stack goes into chimney stack? No insulation on gas flue pipes. Or within 6 inches of 3-4" water heater vent pipes

5) Is insulation fireproof? Everything burns if it's hot enough. If you throw insulation into backyard fire, paper and foil will burn away and insulation kind of falls apart in the heat. Fiberglass insulation cannot be set on fire with a match. Foam pipe insulation will burn.

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.

Electric water heater can be repaired by homeowner.

Four things can cause NO hot water:
1) ECO red reset button tripped. Remove top cover on water heater, push red reset button on thermostat. Put insulation and cover back over thermostat.
2) Circuit breaker is tripped, circuit breaker bad, or wire loose in breaker box. Turn breaker on-off and listen for crackling or fizzing sound, and burned smell. Test breaker for 220Volts. Test top two screws on upper thermostat to see if water heater has electricity.
3) Bad upper thermostat. Replace upper thermostat.
http://waterheatertimer.org/How-to-replace-thermostat-on-electric-water-heater.html
4) Bad upper element. Test upper element.
http://waterheatertimer.org/How-to-test-water-heater-element.html