Mesh bed leveling - Z axis not moving during print

Greetings,

So I have a 3D printer of my own design, hbot with moving Z-axis bed, running the latest version of Marlin. There are two steppers moving the bed up and down via threaded rods.

I recently tried using Mesh bed leveling with a 3x3 grid (with the discount reprap LCD controller) to compensate for a mild tilt in my bed, but the Z axis motors just didn't move to compensate for the tilt during the print. They moved the platform down between layers as it was printing, but not as each layer was being printed.
I also tried using Auto bed leveling with 3 points, using a conductive nozzle probe, but still no luck. The probing goes correctly, the print starts, and the print head runs into the glass on one side of the print, and extrudes a little too high on the other side.

I haven't seen any other forum posts about this particular error, so either I done goofed, or I'm in trouble. Any help is appreciated.

Thanks,

Did you activate the Mesh Leveling?

Try sending M420 S1
this enables mesh leveling in marlin

Quote
Roxy
Did you activate the Mesh Leveling?

quote=obewan]
Try sending M420 S1
this enables mesh leveling in marlin[/quote]
I hadn't tried M420 before, so I just did, but it still isn't running the Z motors. On the bright side, I got a somewhat successful print today, after manually tweaking the Z screws, but it's still a bit uneven.