Help. Impact M3 Plenum will not drain.

Just installed a new Huma extra high pressure regulator on my M3. Installation was easy and by the book. Screwed in the reg adjust screw until it just touched and backed off maybe an 8th of a turn. Screwed my bottle on, plenum fills to pressure set on first reg. Around 180 bar. I unscrewed bottle and tried to empty the plenum by backing out the adjustment screw. Nothing. Then I tried dry firing it. Nothing. Plenum not draining.
The adjustment screw is VERY difficult to turn.
its as though the huma is not working at all.
Is there any other way to drain the plenum so that I can take the reg back out and figure out what is going on? Unscrew gauge?
 
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