Extruder pushing filament out

I've recently built the Prusa i3 from RepRapGuru and it was working fine (with minor hiccups), but decided to change the hotend. The new hotend was not what I anticipated so the original hotend is back on. My problem was with the reassembly. It seemed pretty straightforward, but not the extruder will take the filament extrude a little and then the filament reverses direction. The stepper is continuing to move correctly, but it seems that the extruder is letting go. I suppose I need a diagram to reassemble the hotend, etc. Any help would be appreciated.

The hot-end should have zero effect on the extruder direction. If you mean you changed the extruder then some variants of extruders run in the opposite direction to others. Just change the direction of the extruder in the firmware or reverse the plug on your controller board. I've also noticed that a too high speed in the controller board can cause misreading of signals. I changed from 25000 to 115200 and it stopped playing up. Larry