I have asked about hot water heater running to hot water. Rheem Hot Water Heater, model #81V400 B. Had about 15+ years, never been serviced. Not rusted, no leaks, just started running exstremly hot water. Changed out top and bottom themostats, changed out top and bottom heating elements. Drained tank before changing heating elements.
Every thing done according to instructions. Note: When going to Rheem dealer we were told they do not make same themostat as mine, they gave us a similar replacement. The number on my old Themostat is EWT2L2-1,RI 190f, 2-A70-016-AP10-161 9119... Could this be my problem??

Since the unit is 15 years old it's frankly time to buy another one. You are just pumping money into an old system hoping to save it. The life of hot water tanks varies due to hardness of water and yours has long passed it's useful life. The inside of your tank maybe totally encrusted with build up and you can't see it.

This is a very strange phenomena for a water heater. Let's see if Twink is correct about a build up of mineral deposits.

Turn off water and drain tank. Remove heating elements and reach inside the tank with your finger and feel the surface around the hole. If there is a build up of mineral deposits you should be able to feel it. It would have to be an extensive build up to insulate the water from the tank.

The thermostat actually senses the temperature of the tank, not the water itself. A heavy build up of mineral deposits could be insulating the tank from the water. You may be able to see inside with a flashlight and a small mirror.

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