Rheem electric water heater,model# 81v40dt water warm and here noise coming for water heater

SOURCE: Rheem Hot Water Cylider Thermostat keeps tripping

Sounds like you have a faulty thermostat.  This is the unit that detects the water temperature, and if it is not where it is set, will kick the switch to allow electricity to flow to the elements you replaced. The thermostats are relatively cheap and if you have the knowledge to change the elements, changing these thermostats should not be a problem.

SOURCE: No hot water, Rheem Model RR612T, Electric Hot Water Heater, 60 g

If you don't have current, 0v from terminal to terminal, then you don't have voltage to the elements. Replace the thermostat but check that you have 220v to the thermostat. It is possible that your breakers to the unit are either bad or tripped.

SOURCE: warm water only

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.

SOURCE: Rheem water heater Model 81v40DT

It sounds like the pressure/temperature relief valve is stuck open slightly, and draining out the PVC pipe. This is common in poor water locations.

You can try lifting the release on the top and letting it pop shut again, but chances are good that by now the seat has been destroyed by the water passing over it. Replacements are available at any home store, just remember to drain the water out of the heater so you don't flood the garage. MAKE SURE YOU TURN OFF THE POWER FIRST OR YOU WILL BE REPLACING THE ELEMENTS ALSO! You will need to wrap the threads with teflon tape before installing the new valve.

SOURCE: Rheem 83xr52-2 50 gal residential water heater.

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.