We just got a new hot water tank and since then we have almost 0 pressure on the hot side of our shower. We have a one handle shower unit. I removed the cartridge and checked it out and it seems to be working properly. I am wondering if maybe if with all the air going through the pipes after the install that some crud is blocking the hot water side and if so I am not sure how to get it out.

Remove the cartridge again and then turn the water supply back on for a moment. You might hold a towel over the valve port because the water is really going to spray out but it will flush the lines. This should clear up you issue.