Two possible solutions. I do not have any experience with HAAS machines but this works for Mori Seki and most Fanuc controls.
To make machine back to it's limit stop (home position) in both X & Z use the following.
G28 U0; (For X axis)
G28 W0; (For Z axis)
G28 V0; (For Y axis)
If this option does not work try
Take care on this option as some machines will move to the jobs X0 Z0 first.
In both case's you can execute both on same line, but for saftey it is better to do on single lines. You will also need to sort out in which order you do the moves, normally it is X first. On the Mori Seiki's you can actually define a position on the machine as a second reference position (ie operator sets this in parameters) then by executing G30 U0 etc it returns to same position each time.
Hope this is of help, good luck