Bed crushing into nozzle

out of the blue the bed wouldn’t stop and crushed into the nozzle. Strangely, when I do calibration it does correct job recognizing each corner (I on purpose misaligned them and the printer recognized each corner), I checked all cables cleaned the bed etc. The printer does the calibration correct then crushes into the nozzle. This happened before but calibration would always take care of that, not this time. The printer has been in pretty much continuous use for the past 3 years.

Buildup of an insulating layer of burned plastic on the bottom of the nozzle can prevent the autodetection of the bed contacting the nozzle. Try cleaning the bottom of the nozzle?

thanks, but I have used fresh nozzle and went through calibration process without a problem. I believe the problem is similar nature, and that is when the print starts the nozzle lowers, in some instances, to a spot on the platform that is damaged. Every time the nozzle lowers over the undamaged portion of the bed it seems to work fine. But there is no way to control the first point, I just have my finger on the switch at the beginning of the print, it works fine in about 98%.

Ah, if you’ve got a bad spot on your bed, then you probably need a new bed. Easy enough to swap out (I’ve got two I cycle through).