Z Homing Issues

I'm having an issue homing the Z axis on my printer. The other two axis will home fine. When I turn on the printer, it assumes that it is at 0 on the Z axis. I can move the axis up and down but not below that arbitrary 0 point. When I home the Z axis, the motors hum for a second but don't turn. I've attached the config.h file. Thank you.

try change this:
#define DEFAULT_MAX_FEEDRATE {300, 300, 5, 25} // (mm/sec)

to this:

#define DEFAULT_MAX_FEEDRATE {300, 300, 2, 25} // (mm/sec)

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Steve,

That did seem to make the problem better, but for some reason my printer is moving up when I tell it to home now. Changing the home dir seems to make the problem worse.

It seems that I've fixed the error. I believe I forgot to invert the endstop back from when I was testing earlier.