I have a 13 month old Rheem electric hot water heater and have had nothing but problems. This is my second one in two years. I have hot water in my sink of the bathroom but when I shower, the hot water turns cold very quickly. I've checked the elements and they're fine. I've replaced the thermostat and adjusted it the maximum 150 degrees. The hot water only lasts a maximum of 15 minutes and the second person to take a shower is simply out of luck. I am on quite a budget but have hired a plumber and handyman to look at it but neither has been able to diagnose the problem. Any suggestions or recommendations would be greatly appreciated.

It may be the dip tube broken, If it is 13 months old, you should still have warrant on it check with the manufacturer, good luck

What size is the heater (number of gallons)? I had u upgrade to an 80gal for enough hot water. Read on unit the recovery time. This will tell u when water should be hot again.

If unit is large enough then afaroo is right on.

Chuck

If the elements check good then , as afaroo pointed out) the next place to check is the dip tube. (see image) You show the classic systems of a non functioning dip tube.
Now, as to what caused the dip tube to fail. The tube is secured by a plastic flange under the cold water inlet. If you've applied heat directly to the cold water inlet instead of coming up with a 3/4X4 inch brass nipple you have melted the flange allowing it to drop into the tank. (And I bet the last heater showed the same symptoms too)
Shut the water off to the heater and open the cold water inlet. Is the dip tube intact? Let me know. Tom