G91                                         ; Relative mode
M584 Z2                                     ; Split Z into 2 (Z+U)
G1 Z0 U0 F2000 S1                       ; Move up to 250mm in the +Z direction. S1 to stop if endstop is triggered
G1 Z+2 U+2 F600 S2                          ; Move 2mm in the -Z direction - (I'm not sure what S2 is for?)
G1 Z5 U5 F100 S1                            ; Move slowly 3mm in the +Z direction, stopping at the homing switch
M584 Z2:3                                   ; Join U to Z again (pay attention to drive numbers used)
G1 Z-5 F3000                                ; Move back again 5mm in the -Z direction
G90                                         ; Back to absolute mode