Vanguard water heater 6E722 would only run half tub of water , I figured one of the elements went bad . I replaced both elements , have screw in fuse box separate from breaker box .

There should be a dial to adjust from off to high settings. It would be located front of heater.

1) Buy 3600 watt element. Nothing special needed:
Copy following link to identify type of element:
http://waterheatertimer.org/How-to-replace-water-heater-element.html

2) March 2013: Add a comment and describe the water heater and the element.

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

Hello abcd. Vanguard appears to be manufactured by Rjheem
Rheem promotes that their products require specialized 'resistorized' elements or 'all copper' elements to portion larger brand-specific sales in their pocket and for no other reason.

1) Buy 3600 watt element. Nothing special needed:
Copy following link to identify type of element:
http://waterheatertimer.org/How-to-replace-water-heater-element.html

2) March 2013: Add a comment and describe the water heater and the element.

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

1) Push in reset button, check that unit is receiving 240Volts, test both elements, replace both thermostats:
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html#reset
http://waterheatertimer.org/How-to-test-water-heater-element.html
http://waterheatertimer.org/How-to-replace-thermostat-on-electric-water-heater.html

2) Add comment Feb 2013 and say what you find.

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

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.

You say the hot water runs out after one shower.
You posted under electric heater.

In case you have a gas heater:
With gas heater, the flame quality could be bad because of restricted air flow or dirty burner, the control valve and thermostat could be bad, the air intake could be clogged, or the water heater is full of sediment and the flame is burning all the time and unable to heat much water.

With electric heater, the lower element is probably burned out and bottom filled with sediment, but thermostats could be bad, or you could have shorted wire.

Narrow down the suspects
If water heater makes some hot water then upper element is working.

Three remaining suspects are upper thermostat, lower thermostat, lower element, and possibly a loose wire

Check screw terminals for signs of burning and loose wires. Especially check lower element.

Let's test lower element.
Turn off power.
Remove both wires from lower element.
Test across both screws with a continuity tester.
Continuity tester is available at hardware store, or you can make one with battery, wire and a flashlight bulb.

The continuity tester has a battery and when light comes on, it says the circuit is complete.
Test1) Test across both screws on lower element with continuity tester.
If light comes on then element is good, but element has to pass one more test.
Test2) Test each screw on element to any bare metal part of water heater.
If light does NOT come on with second test, then element is good.
Light ON first test. Light OFF second test. Then element is probably good. But test is not fail-proof without using a meter.

I'm betting the lower element is burned out and you need to replace lower element. And you may need to vacuum out the sediment.
http://waterheatertimer.org/How-to-clean-sediment-out-of-electric-water-heater.html

Now if lower element is good, then the easiest thing is to do is replace both thermostats. Buy generic thermostats at hardware store for $25. After replacing both thermostats, the water heater will probably work. If there is still a problem, then the lower element was not as good as test showed, and it should be replaced also.
http://waterheatertimer.org/How-to-replace-thermostat-on-electric-water-heater.html

If you are still having a problem, answer back and we'll give more details.

1) Turn off power before touching water heater that is shorting or wet or was flooded.
2) Circuit breakers & fuses blow because of heat. A short will cause heat. Tighten screws on terminals inside box, listen for crackling sound/burning smell from loose-fitting parts.
3) Easy test for circuit breakers: move water heater wires to another same-size breaker. If same-size does not blow, then problem is breaker.
4) A short between fuse box and water heater could be gnawed electrical wire. Inspect wire.
5) Wires have size markings. 5500 watt water heater needs #10 wire. 4500 watt water heater needs #10 wire but can work with smaller #12 if distance is not long. See label on side of heater for wattage, voltage, etc. Element wattage is water heater wattage even with 2 elements.
http://waterheatertimer.org/Figure-Volts-Amps-Watts-for-water-heater.html
6) Short inside water heater can be elements or thermostat. Open covers and inspect parts for burning. Screws should be very tight against copper wire. Sediment could fill bottom of water heater cause lower element to short.
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http://waterheatertimer.org/How-to-troubleshoot-electric-water-heater.html

The drain is a plastic valve, looks like a knob with a hose fitting coming out the middle of it. It should be about 1' above the bottom of the tank enclosure.
Be sure to turn the gas off before you drain the water and fill the tank before you relight it.

Quite likely a bad element. There are two in electric HW heaters. Often the bottom one will fail so you only end up with the upper half heated up.

You can check it with a digital volt meter if you have one.

with the power off at the breaker box, you can remove the wires from the element and (using the ohm (resistance) setting) check across the terminals. it should read around (4500W/240V = 18 ohms).

How old a HW heater? might be time to replace it...

Peace,

If it is an electric water heater, there is no pilot light. You could have bad elements or bad thermostats. Be careful working on an electric water heater, as most use 208-220 volts!

If it is a gas water heater, it could be a bad thermocouple, ignitor, gas valve.

My advice to you is to call a qualified service company to come repair your water heater.