Overheating Electric Hot Water Heater

[Grover1949]

My 9-10 year old State Select 50 gallon, 4500W water heater started putting out scalding water and then went cold. I found that the ECO had tripped, so I re-set it. There was a distinct odor like burned bakelite (stronger when taking off the lower cover), so I know something overheated. I went to Menard's and got a replacement upper thermostat with ECO and a replacement lower thermostat. Both are set at 120 degrees. However, the heater still overheats at the top element (I should note that I replaced both elements about 4 years ago). In fact, when it heats up, I get water temps of 140 degrees or more at a faucet. Although the upper element is on, if I adjust the setting, it clicks on and off at near the 140 mark.
I found a 2 year old thread on this board, and went through the steps. Using a good digital multimeter, both elements show no continuity from either side to ground, so I assume there are no shorts. Resistance across the terminals is 13.7 ohms upper and 12.8 ohms lower. There is no voltage across the terminals of either element when both thermostats are set at a temperature lower than the water. When I turn up the upper thermostat and it clicks on, there are 239 volts across the upper element terminals. If the upper thermostat is set below the tank temp and the lower is set above tank temp, there are 239 volts across the lower element terminals.
What confuses me is that any single terminal on either element will show 119 volts to ground, but there are no sounds or signs of heating. How can there be 119 volts from terminal to ground, but 0 between terminals? Is the thermostat providing the ground route when it closes its contacts when it is turned up?
Any and all ideas will be graciously appreciated!
Thanks,
- Larry

[hj]

Water heaters do NOT have a "path to ground", because they operate at 240 volts. Therefore, ALL the terminals will ALWAYS be 120v to ground, but since there is no "demand" for the higher voltage there will be ZERO voltage across the elements, but there will be 240 volts between the two terminals on the lower thermostat, and 240 between the terminals for the upper element on the upper one. As for the overheating water, that we cannot diagnose without being there and making our own tests, which are NOT the same as the ones you are doing.

[LLigetfa]

What confuses me is that any single terminal on either element will show 119 volts to ground, but there are no sounds or signs of heating.

Depending on whether or not the T-stat is closed at the time, seeing half the voltage is to be expected since the panel is fed two legs with a neutral centre tap. You didn't say in what state the T-sats were when you measured the voltage nor did you say haw you came to the conclusion that there are no signs of heating.

Use an ammeter to test for "signs of heating". You could have a short in the wiring to the metal tank causing the 119V to heat the water.

[Grover1949]

Thanks for the input gents! My "sign of heating" was a very low hum when the element was activated (240 across the terminals). I set the lower thermostat a little higher than the upper and the heater is now working fine. Tap water is coming out at 118-120 degrees.