Water is not hot, doesn't last long. Thermostats turn elements on when turned up. Elements show 230 when on.

You will burn up elements if there is no water in the tank when you power it up. There is a temperature adjustment on both thermostats. Most water heaters have 2 elements and 2 thermostats. The temp adjustment is a small white round thing usually, and behind the metal covers on the side.

Testing voltage on heater can be tricky since elements can test 120Volt to ground all all times.
This is because thermostats only turn off 1 Hot leg in the 240Volt circuit, while the other hot leg remains live. Each hot leg in 240Volt circuit is 120Volt.
http://waterheatertimer.org/B220C.html#120-240
Troubleshoot electric water heater:
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html#reset
Try following things in order: Press reset button. Test elements. Replace thermostats.
http://waterheatertimer.org/How-to-test-water-heater-element.html
http://waterheatertimer.org/How-to-replace-thermostat-on-electric-water-heater.html
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If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Problem has to be bad element or bad thermostat.

Test elements for short to ground through metal tank wall:
http://waterheatertimer.org/How-to-test-water-heater-element.html

Make sure factory-installed insulation and cover are re-installed over new thermostats so they do not misread tank temperature.
If problem does not show with elements, then replace thermostats again.

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

Water heater can test for 120V power on elements and thermostats at all times.
That's because thermostats turn off one leg of 240Volt circuit, and not both legs.
You mentioned thermostats and elements, implying two elements and two thermostats, so your water heater is 240Volt.
240Volt breaker might be bad on one leg.
Open following links to troubleshoot
http://waterheatertimer.org/Test-electricity-to-water-heater.html
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

Yes the water heater has a dip tube.
http://waterheatertimer.org/How-it-works.html

Marathon elements are specific to that water heater and can be ordered online, but generally are not at the local hardware.
Good to keep a couple spares around.
Marathon is 240Volt water heater.
Thermostats turn off one leg of the 240Volt circuit, so elements and themostats will always test for 120volts.
You removed wires off elements and tested each for continuity and tests showed elements to be good.
Test top two screws of upper thermostat and make sure you are getting 240V to the water heater.

If water heater has some hot water, then that says water heater is getting 240V, upper element is good, and remaining suspects are bad thermostats, bad lower element, or sediment build-up, or combination.

Open following link for troubleshoot run-down:
http://waterheatertimer.org/How-to-troubleshoot-electric-water-heater.html

Water well.
If you have sediment build-up that reaches lower element, then water does not circulate around the element and water heater no longer heats very fast or accurately. If sediment is the problem, sooner or later the lower element will burn out.
Doesn't hurt to flush out the tank now and then, and vacuum out the sediment if that is problem.
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html

Not knowing how old the unit is, it's possible that both elements could be bad, especially if you ru out of hot water quickly. If your sure the breaker is okay and you know how to use a voltage meter. Check the voltage at the thermostats and elements. While you are looking at the thermostat(s), press the red reset button and give it about 5 minutes and see if you hear the water heating up. If you have voltage at the thermostats and the elements. Turn the power off and check for continuity through the elements. If you don not have continuity, the element is bad. If all seems to check out, you probably have a bad upper thermostat. Check all connections and inspect the wires.

1. Check and see if the thermostats are getting power.
Remove cover (access Door) Test the leads for power
2. If there is power at the thermostats try hitting the reset button on the top thermostat
3 Check and see if there is power at the element
4. To tune up your water heater is an easy job ... You can buy thermostats for less than 15 bucks and elements cost 8 dollars at lowes or home depot. Remember to kill the power when working on the unit. It is 220V It will kill you !

Disco Power
Turn water off
Drain Tank
Remove wires to Elements ( Remember to match the amps on the elements !) If they are 3500 replace with 3500 etc.
take a wrench and remove elements and install new.
next replace the thermostats wire exactly as you see them

This project costs 30 dollars and makes your water heater new again !
DO NOT TURN POWER ON BEFORE THE TANK IS FILLED

Open the faucets in the house when they quite blowing air the tank is full !

Here is a manual for your water heater, I think it's actually an 82VH40-2
http://globalimageserver.com/fetchDocument.aspx?id=17bb6286-4eb8-4e44-813e-6ccfafda4404

An electric water doesn not have a "thermocouple" like a gas water heater does that senses pilot., Most electric hot water heater has two heating elements, two thermostats, with high temp cut outs. If your heater is not working, the elements could be bad. If you want to test, remove power to the water heater, disconnect wires from heater elements, and using an ohm meter measure resistance across the terminals. If it is open then the element is bad. You can compare readings from top and bottom elements. While the bottom element is on more often, if you're replacing one, I'd replace both. The water heater will have to be completely drained in order to do this. If the elements are ok, then you can test the thermostats the same way. It would have been better if you could have described your problem

Check the elements, if you have access to a meter to check them. If they are getting power to elements and you have no hot water.
The elements are not working correctly. I had some elements check out ok till the thermostat's turned on and the elements didn't heat.
Sounds like the elements are bad.

If this all of sudden happened and you had hot water. Check for power to the heater and to thermostat. Thermostat may have tripped out to reset it just press red reset button on it.

If you have done all this and you have power to heater, thermostats and to the elements. Then the elements need to be replaced and you need to turn off power and drain heater before changing elements out.

I hope this will be some help to you.