Increasing air charge of already-installed expansion tank

[Jadziedzic]

Our house's PRV was replaced a few weeks back and everything is working OK, but I'm thinking the plumber probably did NOT change the pressure in the expansion tank in the system. (I think the tank is probably around 50 PSI air charge, with the PRV set at 70 PSI.) If I turn off the water and release any pressure in the pipes will allow me to properly set the air charge in the expansion tank, or do I need to fully drain down the system?

 

[Reach4]

Yes.

Just drop the water pressure to significantly below the air precharge. Turning off the water, and opening a faucet should do that. No draining needed.