For detailed user manual of Repetier Host, please refer to Wiki:
http://www.geeetech.com/wiki/index.php/Repetier-Host
8.4 Possible causes for motor’s no-action
http://www.geeetech.com/forum/viewtopic.php?f=13&t=17038
8.5 Extruder does not work normally
http://www.geeetech.com/forum/viewtopic.php?f=13&t=17097