Auto Bed Levelling Switch Not Working

Hey,

I am wanting to see how auto bed levelling works on my printer before I get servo's and all that jazz, so I simply made a mount for a push button and swapped it with my extruder.

I am using Marlin - Jcrocholl's version.

Now, I have found something very odd!

I have all the inverting and all that set up correctly as my button is N/O rather than N/C.

When I do a straight G29 it goes through the motions and the button works, however as it isn't homed it starts off in the centre and moves all over the place!

When I do home it with a G28, then do a G29 it lowers it's self but doesn't stop! It doesn't even stop when I press the button manually!

This has puzzled me, and I am sure there must be a setting I have got wrong somewhere!

Thanks,

Alex