Your testing may be off here. Or you might have special order 'simultaneous' wired water heater.
Water heaters with two elements are 240V.
Elements test for 120V at all times, but with ordinary non-simultaneous water heater, only one element at a time has 240. This is called non-simultaneous operation.
Open links below for understanding of water heater operation.http://waterheatertimer.org/How-it-works.htmlhttp://waterheatertimer.org/How-water-heater-thermostats-work.htmlhttp://waterheatertimer.org/B220C.html
If both elements were drawing 240 at one time, then upper thermostat is bad, or else your water heater is wired for simultaneous operation, and one of the elements is burned out.http://waterheatertimer.org/How-to-test-water-heater-element.html
Your tank might be wired for simultaneous operation, if water heater was special order from Rheem, or if somebody changed wiring and set lower thermostat-and-element on a separate circuit breaker.
If you have simultaneous operation, then you would have 2 circuit breakers and 2 wires going to water heater or one 50 amp breaker with 8 gauge wire to heater. If this is the case, then both elements could test for 240V and one of the elements is bad, and thermostats are ok.
If you have ordinary Rheem water heater, then it is wired for non-simultaneous operation where only one element is ON at a time. This is called non-simultaneous operation and you can check because water heater has one circuit breaker rated for 20 or 30 amps.
Rheem elements are 4500Watts.
If both elements were ON at same time, that would be 9000Watts, which would trip typical water heater 20-30 amp circuit breaker.
9000Watts divided by 240 volts = 37.5 amps
So if upper thermostat is bad, and it is turning on both elements so they both test for 240, then thermostat is bad, but also one of the elements has to be bad.
Or test is inaccurate.
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