I can't get my new water heater to fill up unless I turn on the water and leave it running at the sink inside the house?

Who put the new water heater in? How do you know it's not filling as it's supposed to?

Hi Lesamj

That's how it works, friend. You must displace the air from the tank in order to fill the tank with water and the only way to do that is to open a faucet (or the T&P valve on the side of the tank) and replace the air with water. When water flows cleanly out of the faucet, without sputtering, then you tank is full and you are all set to turn on the electricity (if electric) or light the pilot (if gas) and you are done!

Mark