Hi,
if you are using mm units why are you describing in inch units?
Lets establish a few basics.
If you look on the Output LEDs panel on the Machine Diagnostics panel does the Probe LED light up when
you manually touch the plate? If not your probe circuit and/or connection to your BoB/controller is faulty
or you have not correctly assigned the port and pin to Machs probe input signal.
To establish whether G31 works jog to over the top of the touch plate, about 2mm above the surface.
<Zero> the Z axis.
Now MDI G31 z-5 f100.
The machine should lower at 100mm/min until it touches the touch plate and stop.
Were you to check now the value of the pound variable #5073 it should contain the current Z axis coordinate relative
to the Z=0 you started at.
Craig