Hey, I bought the same exact one and was having the same problem. There is a set screw that is most probably set to high from the factory. I thought that when I turned the middle knob all the way toward the minus sign that I would be at 0 PSI, but mine was actually set from the factory to be at 20 PSI. Once I took that set screw out it allowed me to zero out the pressure. It's a tiny Allen wrench screw. Hope this help.