Overheating Electric Hot Water Heater
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!