Top heating element was broke. Replaced got hot water for week. Now have to run hot water for 20 mins before it goes from warm to hot. Top heating element reads 240VAC bottom heating element reads 99VAC. Rheem 50 gallon tank Electric

5 years is about the lifespan for tankless.
You might have shorted element. That would explain cooler water and tripping reset.
Test element: power is off, disconnect wires from element; ohms = voltage squared divided by watt rating of element
http://waterheatertimer.org/How-to-test-water-heater-element.html

Call service technician./ Call Bosch
http://waterheatertimer.org/pdf/Bosch-AE115-AE125_manual.pdf

Gene

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

top element fried unless temp was met at time of test

Hello Bill The temp stat is a square box clipped in under the elements .Can be replaced in 5 minutes.Need a large flat screwdriver.

The top element only comes on when the heater is about out of water. The water is directed to the bottom of the tank. Cold water stays on bottom, Bottom heater element heats water. If you use all that water then the top of the tank gets cold and the top element comes. When the top of the tank is warm, then the bottom element comes on. I would susupect the bottom element as it does most of the work. If you have an ohm meter, turn off electric, and remove wires from element. Check element for continuity. If you don't get reading, then that element is bad.

Warm water is a result of and element gone out and more than likely top element is gone out. Best thing is to replace both element's because they are not exspensive and if you replace just one it will work the other one harder and eventually go out.

Just a little information if the bottom element goes out it will give you a burst of real hot water then get cold. If top element goes out it will give you warm water then get cold.

Thermostat may be tripped out or breaker tripped that would be the first few thing's to check. If they check out maybe the element's are in need of replacement.
The clue with element's is one will go and the other will follow. The top element goes you would get luke warm water till the bottom goes out. The bottom goes out first you will get a blast of very hot water till the top element goes out.

Check out this link for further information on water heater trouble shooting.

http://www.water-heater-repair-guide.com/electricwaterheatertroubleshooting.html

Some elements will read with a meter good until they heat up.

Hot water then going to ice cold top element is working and bottom bad. Luke warm water and then goes cold bottom element good and top element bad.

Elements and thermostats are not to exspensive to replace.

If you have power only two thing's left are the thermostat's and the elements.

Sounds like bottom element may be bad but usually reads open circuit if bad. Also tan k would run about 8 gallons hot water then go cold. lots of warm water usually means bad dip tube.
Check if tank is hot at bottom element when not used for a while. If bottom element is still cold then bad element.
If bottom element is hot - (all water in tank is hot then you have a bad "dip tube" This is allowing incoming cold water to mix with outgoing hot water. The dip tube is usually A part of the cold water nipple or B located under the cold water inlet nipple.

Hi,
You did not specify here so I'm guessing... you have an electric hot water heater.
The problem that happens with them is that the bottom element goes bad. The top one still works so you still have hot water, just not much of it.
Usually when the top element is satisfied it switches to the bottom and heats the rest of the tank.
I think you will find that your only heating the top 1/3 of the tank and that the bottome element needs to be replaced.

I hope that this will help you to solve your problem!

Thanks for using Fixya!!

Heatman101

You can eliminate the shower control knob possibility by turning on your hot water anywhere else in the house. If you get hot water in other places, then it could be the knob causing it. A substantial lime buildup in the tank can also cause poor heat transfer from the elements to the water.