Lower elements not working - Frigidaire 24 in. FDB750RCC Stainless Steel Built-in Dishwasher

sounds like you got a defective element

time for a new element

When the top of the tank is hot the upper thermostat removes power from the upper heating element and transfers the power to the lower thermostat and heating element. If the lower thermostat is defective, then the lower portion of the tank will not be heated and the supply will be greatly reduced. You replaced both elements however check that the lower element is coming on after ther upper one cuts out and is acutally working.
Check for power at the upper thermostat terminals where the power is sent to the lower thermostat and heating element. If there is no power then the upper thermostat should be replaced. If there is power then check for power at the lower heating element. If there is no power at the lower heating element then replace the lower thermostat.
If there is power to the lower heating element then it should be getting hot. If it is not, maybe defective. Another possibility is a broken dip tube. Check for a broken dip tube and replace if necessary.

If the dip tube is broken, the incoming cold liquid can mix with the out going hot liquid and cause it to seem as though you are running out.

your element is bad replace element.

You need to take 1/2 hour to learn basics and then test water heater parts before replacing anything.
http://waterheatertimer.org/How-to-troubleshoot-electric-water-heater.html
Follow the troubleshooting steps, and it will tell you exactly where the problem is.
Otherwise we can guess at 20 different things.

Water heater is 240V because you have more than 1 element.
Did you test for 240V across top two screws of upper element?
Breaker can be tripped off on one leg and 120V arrives at water heater so heater looks like it has electricity, but circuit is not complete.

The problem can be loose wire, bad 240V circuit breaker, sediment reaching lower element, bad thermostat, bad upper element, tripped ECO reset button.

Did you replace factory insulation and cover over thermostats after replacing elements?
Did you vacuum out sediment when replacing lower element?

How long ago did you replace elements? If you turned power ON before tank was completely filled with water, then you burned out the element. If upper element is burned out, the tank has no hot water, even if lower element is good.
Test the upper element:
http://waterheatertimer.org/How-to-test-water-heater-element.html
See how a water heater works:
http://waterheatertimer.org/How-it-works.html

And finally, why so many folks write to fixya saying they replaced both elements and upper thermostat, but they never replace lower thermostat for another $6? I have been puzzled about that since lower thermostat turns on and off each time tank temperature drops and is responsible for keeping water warm during standby hours. Lower thermostat cycles more times than upper thermostat.

Add a comment if you need specific assistance with any of the testing steps.

Electric water heater can be repaired by homeowner.

Water heater has some hot water.
We know 3 things for sure:
- electricity is ok
- upper element is ok
- tank does not have overheating problem

Here are the suspects:
- Burned or loose wire
- Upper thermostat not working
- Lower thermostat not working
- Lower element not working

What to do:
1) Turn off power, open water heater covers and look for signs of burned or loose wire, especially on lower element. Burned wire on lower element says lower element is burned out.

2) Test lower element.
Lower elements burn out when sediment builds up inside tank.
http://waterheatertimer.org/How-to-test-water-heater-element.html
http://waterheatertimer.org/How-to-replace-water-heater-element.html

3) If wires are ok. And you do not want to test parts, then replace upper and lower thermostat for 25$. If problem persists, replace lower element.
http://waterheatertimer.org/How-to-replace-thermostat-on-electric-water-heater.html

4) If you want to test thermostats and elements before replacing anything:
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

5) When finished, be sure to put insulation and covers back on tank so thermostats don't receive cool air and misread tank temperature. This will prevent overheating of tank that causes red reset button to trip.

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

http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

You have a 240V electric water heater because you have an upper and lower element

The upper thermostat works in the manner you have discovered.
In residential electric water heaters, the upper element is ON or the lower element is ON, or both elements are OFF.
This is called non-simultaneous operation.
Non-simultaneous operation means the elements are never turned ON at the same time.

Because water heater thermostats only turn off one leg of the 240V circuit, the upper and lower elements will always have power on the two screws, but not across the two screws.
This power is 120V and the circuit is not complete so the element will not heat.
So if you test any element, it will always show at least 120V
Only when the thermostat clicks ON is the 240V circuit completed, and the element turns ON.

Identify the problem:
1) The shortage of hot water is caused by a bad upper or lower thermostat or a bad lower element.
We know the upper element is working because you have some hot water. If the upper element was burned out, you would have no hot water because the upper thermostat would never click over and send power to lower part of water heater.

2) It sounds like your upper thermostat is clicking on and off, so I would test the lower element.
http://waterheatertimer.org/How-to-test-water-heater-element.html
http://waterheatertimer.org/Do-it-yourself-water-heater-timer.html

Add a comment if you need more information, and I will help.
The do-it-yourself link above will give you full electrical how-to for self-fixing electric water heaters.

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.

If original problem was caused by sediment burning out lower element, did you clean sediment out of water heater when changing lower element?
Two element water heaters are 240V.
Thermostats cut power on one hot wire, but 240V circuit has 2 hot wires. So lower element has power at all times coming from the red wire.
1) Use ordinary tester or multimeter set to 240V <> test each screw of lower element to bare metal part of water heater. Each screw should show 120V. If there is no power, then upper thermostat is defective, screw on upper thermostat is loose, or red wire between upper and lower parts of water heater is bad.
2) Remove wires from lower element. Use continuity tester or multimeter set to ohms <> test across both screws of element to see if power travels through element <> if element is bad, then continuity tester will not light up and multimeter will show no ohms. Put wires back on element after test.
3) Start with cold water in tank. Turn on water heater & upper element will turn on. Put ear on side of tank to hear if upper element is heating water. Test #3 screw to #2 screw on low left side of thermostat, should read 240V > Test #3 screw to #4 screw on low right side of thermostat, should read 0V.
Put ear on side of tank. When upper element turns off: Test #3 screw to #2 screw on low left side of thermostat, should read 0V > Test #3 screw to #4 screw on low right side of thermostat, should read 240V. If this test shows 0V and 0V, then upper thermostat is bad. If reading is correct, immediately move to next test.
http://waterheatertimer.org/images/Thermostats-numbered-divided-500.jpg
4) Turn temp on lower thermostat to 150. Using ordinary tester or multimeter set to 240V <> Test across both screws of lower element. If there is no reading, and you know element is good from step 2, then lower thermostat is bad, or wire is bad between lower element and lower thermostat, or wire is bad between lower thermostat and top part of heater.
5) Test across both lower thermostat screws, should read 240V.If this test is good, it means wires are good. Put jumper wire across both screws of lower thermostat, and test lower element again. If element finally turns on with jumper wire, then lower thermostat is bad.
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http://waterheatertimer.org/How-to-troubleshoot-electric-water-heater.html

If wire is bad between upper and lower parts of water heater, and water heater has tight-fitting 2" foam insulation, it usually indicates water heater replacement.