i have just restarted the printer and now my z-axis drives up to the sensor, registers but doesn't do the 4mm back off and is convinced it's at Z0 but is infact 4mm above the bed!! Any help!?!?
Update: For future reference it appears the BigBox was waiting for me to level the bed? Not sure why it normally homes just fine.
You need to go in and Store to memory after running the bed leveling wizard. Try M500 from g-code if the LCD isn't doing what you like
I was experiencing something similar, despite having done the "store memory" step after bed leveling. Another user suggested it might be because the IR sensor was seeing the edge of the glass plate, and that was throwing off the Z-homing. So I backed out the X-axis end stop screw a bit, and that seems to have fixed the problem for me. Now I can power down the printer, then power it back up and have it auto-home reliably.