Jadnashua
Retired Defense Industry Engineer xxx
You do not need to turn the WH off, or drain anything out of it most of the time. Just go to say the kitchen sink and open the valve and leave it open until you've pressurized the tank properly. To check the static pressure, do that before you shut of the main water feed to the house. Unless the WH outlet is higher than the valve you open, all that will happen is you relieve the street pressure, and it won't drain. If, which does happen, the WH is above, say in the attic, THEN, you'd want to shut the WH off, as it could drain via gravity when you open a valve. In most places, that won't happen, but never run a WH if it is not full of water - so, you could turn it off to make sure it didn't try to turn on while not full, but in most circumstances, it's not necessary. Location of the WH, and the type of house vary, but where I live, almost everyone has a basement, the WH is there, and if you open the faucet on the first floor, the only water you get out is from leaks from above on the second floor, and a dribble as the street pressure is relieved. Your results may differ.
As long as the system isn't pressurized from the street, and won't become that way when you add air to the ET (say that sink faucet you left open), you can deal with it.
As long as the system isn't pressurized from the street, and won't become that way when you add air to the ET (say that sink faucet you left open), you can deal with it.