I got a setup with one prefilter (in the canister) and 3 filters. While i was there working on something else i was asked to replace the prefilter since he had it, but couldn't get the old one out..

So i shut off the incoming line, push in the pressure relief button in, opened the drain line in it also. put on the wrench tool it came with and try my hardest to budge it, even had the owner to turn it by had while i used the wrench..

WTH

Ive never ran into this before.

I even took off (or broke) the red button on top that releases the pressure, its just a red button with a spring in it, and i couldn't figure out how to get it back in.