No hot water just cold

most water heater of that size is rated 240v, therefore it needs 2-pole. is it 240v rated? make sure you have a properly sized circuit breaker & matching conductors (wires) with the kw rating of the water heater

No.
Fold-back elements are low-watt-density, so element does not burn out as easily since heating is spread across more surface area. But recovery remains 16 gallon per hour.
20 amp breaker and 12 gauge wire: max 3800 watts
30 amp breaker and 10 gauge wire: max 5800 watt.
4500 watt element heats 20 gallons per hour.
http://waterheatertimer.org/How-to-replace-water-heater-element.html
http://waterheatertimer.org/Increase-amount-of-hot-water.html
Instead of changing elements: Set thermostats higher so more cold is added to hot water, and then you have more hot water available inside tank.
Gene

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

Maybe more than 1 problem: Suspects are: crossover, sediment or assorted gunk is built up in bottom of tank, or a loose wire or bad circuit breaker, or loose connection somewhere at water heater.
There is no off-peak setting unless you wire up the water heater differently or install a timer.

1) When water is cold, open TP valve at hot water heater to see if tank has hot water.
If tank has hot water, but it does not arrive at faucet, then suspect is crossover:
http://waterheatertimer.org/Crossover.html

2) To test if circuit breaker is problem, move wires to different circuit breaker with same amp rating:
http://waterheatertimer.org/B220C.html
http://waterheatertimer.org/How-to-replace-circuit-breaker.html

3) Turn off power, open connection at top of heater and check that wire nuts are tight
Check all wire connections for signs of high heat and burning.

4) If bottom is filled with gunk, the lower part of heater can be slow to heat and will take so long that top part of heater will cool. Clean sediment out of tank.
http://waterheatertimer.org/How-to-clean-sediment-out-of-water-heater.html

I'm thinking when you say black box, that you also have a wall switch with a symbol like a lightning bolt and you switch that on as well as checked breaker panel to make sure breaker is on as well.
With that said, you'll have 2 of 3/8" nuts holding that black cover on. Remove top one and loosen bottom one and pull cover off. ( Be sure power is off to unit while doing this.) You'll find the element in behind it. Put a voltmeter on black to element (red probe or alligator clip) and (black probe) to ground where you see green wire connected to tank. Turn breaker on then switch at wall. You should hear a relay click and 120 Volts should show at black wire ( red probe) . If you've got 120 volts there, shut off all power, drain water heater and replace element.

Tough problem here. Most dual element heaters share one line. if this is the case and you have power on the top and none on the bottom I would check the connecting wires one to another. also check the settings of the thermostats. They may be adjusted all the way down. If the wires and connections are good I would recommend ohm testing the new elements. I have burned elements out by introducing cold water to very hot coils (forgetting to turn the water on after flipping the breaker)
Never forget that calcium buildup will short the element. If touching on the bottom you will burn it up.
If this does not help try borrowing hot water from neighbors ;)
Good luck
Joe

You have electric water heater.
You replaced elements and thermostats but heater still won't work.
And tank was completely full of water, and water was running out of a faucet before turning power ON.
If elements are not fully immersed in water, they will instantly burn out.
If upper element is burned out, then tank will have NO hot water.
If lower element is burned out, and upper element is not burned out, then tank will have some hot water.
http://waterheatertimer.org/How-to-test-water-heater-element.html
http://waterheatertimer.org/How-it-works.html

If elements did not burn out, then that leaves 1 main suspect: the electricity.

1) Push in ECO red reset button on upper thermostat. If ECO is tripped out, then heater will not work.

2) Click circuit breaker all the way one direction and then back the other direction to make sure breaker is latched.

3) If tank has 2 elements, then it is 240volt.
If 1 leg of 240Volt circuit is not working, then 240V appliance will not work.
240Volt circuit needs both hot wires to complete the circuit:
http://waterheatertimer.org/How-to-wire-EH40-hot-water-heater-timer.html#120-240

Buy cheap multimeter from Home Center and set dial to 240-250-277VAC
Tape tester leads to woods sticks to keep hands away from power.
Power is ON
Test across top 2 screws on upper element should show 220-240 volts.
If you have 240 at top two screws, then skip down to step 6.
If no reading across top two screws, then move to top of tank.

4) Open connection point where wire connects to heater.
Test across both insulated wires should get reading of 220-240 volts.
If no reading, move to circuit breaker box.

5) Mark water heater breaker.
Turn off all breakers except water heater breaker and main breaker. (and breaker to light fixture where box is located)
Do not hold or touch or lean against anything metal.
Stand on dry boards and wear dry clothes.
If main breaker is OFF, the big wires that connect to main breaker are still HOT.

Remove box cover.
240Volt breaker has 2 wires connected with screws.
Test across both screws for 240Volt.
See if wires are loose.
If there is no reading, then breaker is not working on one leg.
To double check, move water heater wires to another same-size 240V breaker and then put ear against water heater to listen for bubbly-fizzing sound.

6) If you are getting 240 to water heater, then wire inside tank could be loose.
Do 30 minute troubleshoot:
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

Add a comment for more free help.
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For a price, fixya expert speaks with you over phone while you work on timer.

First of all, you have 240V water heater because tank has two elements.
You have no hot water, and tank has power to upper element.
Lower element has no power.

Something doesn't sound right.
You're not testing correctly.

Before doing anything, test across top two screws of upper element for 240Volts.
This will eliminate electrical problem as suspect.
Breaker must deliver 120V on both legs to complete the 240V circuit.
Every single-phase household circuit takes 2 wires to complete the circuit.
With 120V you need 1 neutral wire and 1 hot wire to complete circuit.
With 240V you need 2 hot wires, one from each hot busbar, to complete circuit.
Your water heater can appear to have electricity if breaker is delivering power on one leg of the 240V circuit.
To check breaker for sure, move wires to another similar size breaker to see if water heater functions properly.
http://waterheatertimer.org/B220C.html

If 240V circuit is good, then next thing is take 30 minutes and do full test of water heater parts.
This will identify exact problem(s) without guessing.
Buy 5$ multimeter from Home Depot. Install battery.
When test calls for continuity, rotate dial to Ohms (upside down horseshoe is ohms).
When test calls for testing voltage, rotate dial to 240-250-277 VAC
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

Add a comment for more help.

Your water heater has 2 elements so its 240Volts.

1) If breaker is delivering power on one leg of the 240Volt circuit, then water heater can appear to have electricity, but tank is receiving 120V. Both 120Volt legs are needed to complete the 240V circuit. Double check for 240Volts.

2) Review electric Load.
Water heater label shows wattage of tank.
If tank is 4500Watts for example, you installed 3500 or 4500 watt elements.
With 5500 Watt elements you need 30 amp breaker and orange-colored 10 gauge wire
With 4500 Watt elements you can get by on 20 amp breaker and 12 gauge wire up to 75 feet away.

3) Check ECO red reset button on upper thermostat. If reset is tripped, then ECO is reading high temperatures. Suspects at this point are defective upper thermostat, shorted wire or bad lower element.

4) Also note that insulation and cover must be re-installed over thermostat. Thermostat reads temperature through wall of tank. If outside air circulates around thermostat, that can cause a mis-read and cause tank to overheat and ECO trips.

If you don't want to test the heater, replace both thermostats for about $25. Return the upper thermostat for a refund. Then see of problem persists.

Here's what I would do.
1. Check breaker for 240
2. Check water heater for 240 across 1 and 3 screws on upper thermostat
3. Note wiring and breaker size.
4. Note label on side of tank.

5. Look at end of new element to see wattage printed on each element. Look for sings of high heat and burning. Tighten screws on elements.

6. Check ECO reset button. Look for high-heat and burning. Tighten screws on thermostat.

7. Test upper thermostat as follows:
http://waterheatertimer.org/images/Electric-diagram-water-800.jpg
Test left-side #1 screw to right-side middle #4 screw. Test should read 240V at all times. If not, then ECO is tripped, thermostat is bad, or electricity is OFF

8) Water heater is cold so upper element should be ON. Test upper thermostat.
Test right-side #3 screw to left-side bottom #2 screw and it should read 240V
Test right-side #3 screw to right-side bottom #4 screw and it should read 0 volts

8. If upper thermostat checks out. Test upper element for 240 across both screws. If upper element does not read 240 when water is cold, then element is bad or there is a shorted wire between element and upper thermostat.
How to test element:
http://waterheatertimer.org/How-to-test-water-heater-element.html

9. Do a full troubleshoot on electric water heater
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

If the lower heating element burns out the upper element will heat the top part of the tank then shutoff. homw depot/lowes etc should carry elements. 1 turn off breaker, remove element access cover (the 2 panels on the front of the heater) test for electricity at the reset button ( uppermost device in upper panel) to make sure power is off. 2 turn off water (I usually turn off the cold water main to stop water cross feeding into hot supply line back into heater) 3 disconnect the 2 wires on the lower element, test with continuity tester. shhould be no continuity between terminals and tank, but around 10 ohms between the 2 terminals. Check the thermostat for continuity if tank is cold thermostat should be closed ie zero ohms across the 2 terminals.
If stat is bad replace stat; disconnect wires push it up out of the spring clip insert new stat reconnect. If element is bad: drain tank. connect garden hose to tank drain valve, open tank drain valve turn water main on to clear rust sediment and get water flowing. Next remove filter screen from a hot water faucet then turn on ( a hot faucet upstairs or higher than tank drain). Now turn water main off, air will now go in through hot faucet and tank will drain, takes about an hour. Use a water heater element wrench about$10 to remove element(s) make sure no bits of rubber gasket are left in element opening- dig em out with a screwdriver if needed. Insert new element with its gasket and tighten. reconnect wires DO NOT TURN ON ELECTRICITY! BE SURE TO FILL WATER HEATER WITH WATER ! Turn water main back on -air will come out of the hot faucet for several minutes. When water runs without any air sputtering, turn off faucet and replace the faucet filter screen. check element(s) for leaks. turn breaker back on.

Your upper element is burnt out. open top cover, turn power of at breaker panel,drain hot water tank . remove black and red lead wires from the element use a socket to un thread the 3000watt 240 volt screw in element. re install the new element atach wires to element. Fill tank with water before turning on power or you will be replacing both elements very shortly