I would just like to add to this. I have just commissioned my printer with the Duet WiFi. Same issue. Same fix by editing the homeall.g file.
This is working:
G91 ; relative mode
G1 Z4 F200 ; raise head 4mm
G1 X-300 F3000 S1 ; move up to 240mm in the -X direction, stopping if the homing switch is triggered
G1 X4 F600 ; move slowly 4mm in the +X direction
G1 X-10 S1 ; move slowly 10mm in the -X direction, stopping at the homing switch
G1 Y200 F3000 S1 ; move up to 240mm in the +Y direction, stopping if the homing switch is triggered
G1 Y-4 F600 ; move slowly 4mm in the -Y direction
G1 Y10 S1 ; move slowly 10mm in the +Y direction, stopping at the homing switch
G1 Z5 F6000 ; Raise Head 5mm
G1 Z-325 F1800 S1 ; Move Z down until the switch triggers
G90 ; Back to absolute positioning
G92 Z2.5 ; Tell the firmware where we are
Firmware Name: RepRapFirmware for Duet WiFi
Firmware Electronics: Duet WiFi 1.0
Firmware Version: 1.18.1 (2017-04-09)
WiFi Server Version: 1.03 (ch fork)
Web Interface Version: 1.15a