I just replaced my hot electric hot water heater. And since I replaced it, I can only get about ten minutes of hot water and then it goes cold. I checked for power to my top element I had 240 volts. I checked the resistance of the upper element and it was only four ohms. The bottom element is 18 ohms. I then unhooked the power and ground wires from the hi limit controls and the resistance of the upper element went to 18 ohms as well. Is this normal?