When it's screwed down completely, is it loose? Does it wobble in the
thread?
Take a look at the bottom of your Protank and see how far the center post sticks out. Then look at your other
tanks and see if they're ~ even with the protank. My theory is that the Protank is slightly more recessed than the others, or the center pin on your VTR is depressed slightly.
I don't have specific knowledge of the VTR, but this has happened to me. You've got 2 options: Since you just got it, you could run an RMA, contact your vendor and ask for an exchange because it's not working, or for them to look at it. It'll probably take a week or two.
The other option is that you could take a small screwdriver or knife and gently try to pry the center post up so that it'll make contact. The center post on the
device is just sort of floating with a gasket around it, so it'll move if you give it a little pressure.
Take your blade/screwdriver and gently work your way around, prying up, gently. Gently. You only need to move it a few millimeters. After you go around once, screw it back in and check it again.