Z Axis Homed Then moves wrong up or down
New to 3d printing period, built a reprapguru V2 which has the arduino 2560 & Ramps 1.4 with marlin 1.8.3 installed. So I've been looking all around just trying to get this thing to run right and I almost have it good but I am stuck currently. Basically, after I home the Z, to which it will travel down and hit the endstop just fine, but after that if I hit the manual control to move it ether up or down using the .01, .1, 1 or 10 buttons it automatically starts to move down towards the endstop. I am not sure the exact distance but its equal to about 3 inches of travel. I was looking through the code in marlin and couldn't see anything out of the ordinary (Im new to c++ however) and there is no home offset in the eeprom settings. Also, the X and Y don't have this problem, can anyone offer a suggestion?