Time to get out your voltmeter and check for battery voltage across the two pins on the monovalve,this should be done with temp wheel on min. and center button pushed on pushbutton assy.
If you have 12 volts across these terminals valve should be closed.
I saw in your post that mono valve core was recently replaced,if the steel sleeve around the magnet coil is not properly aligned (there is a notch that should align with the point where the magnet wire comes through) it can cut the magnet wire.
if the wire is cut it's time for a new assy.