You need to get the tank 100
percent full before you turn the power on or you
may burn the top element on the water heater
I have seen this happen so many times. You turn the water on you hear the water stop running into the water heater and you assume it is full, but it is not, air gets trapped in the top of the tank. you need to run a faucet on the hot side until you hear all of the air come out and you get a steady flow of water before you turn the electric or gas back on.