I've built a DIY 3D printer similar to Prusa i3. It does homing and bed leveling very well with a PNP Lj12a3_4_Z_BY sensor using G28 and G29.
However, when I push the print button on Pronterface or Simplify3D, Z axis goes up about 20mm and starts printing in air. I can't figure out what is going wrong.
