[HayZee518]

the power input to the heater should be 240 volts. check the top two screws at the upper thermostat, it should read 240. if it isn't go back to your panelbox and look at the breaker(s) feeding the tank. the breaker should be a two pole breaker. sometimes two single pole units are installed with a plastic tie-bar across the two breaker's handles so if one trips it takes the other with it. if this is not the case then put in a tie-bar. across each operating element you should read 240 volts NOT the 120 you state. True, from each leg to earth ground you'll read 120 volts but the elements are meant to operate at 240 volts.