BLtouch 3d grinds on plate

[Burningz]

I'm having all sorts of trouble with the bltouch - I assume i put the nozzle to the plate with the bltouch with the pin in and then shift it up till its say 3 mm off the plate. When i do home or level the nozzle grinds into the plate as though its been told to keep pushing down. Ive looked at the videos and oddly have had it working before (got sick of 3d printing but recently dusted off my geeetch a20m to start again). what am I doing wrong? Thanks for any help

PS - or alternatively show me how to remove it from firmware (eg where to look for original firmware minus bltouch I added later)