I have a Rheem 50 gallon electric water heater model 81VR52DT. Setup with Therm-o-Disc thermostats double element non-simultaneous operation. Problem is that lately we are running out of hot water. Both top and bottom elements have 20ohms +/- resistance (measured with a Fluke 8060a). The bottom element did not have voltage to it during testing. I don't understand why there is 'non-simultaneous' operation.
Appreciate any help.