The gap between nozzle and printed layer is too big

Hi everyone,

My printing problem is that after printing a few layer the nozzle doesnt touch the previous printed layer anymore, another word is the gap between nozzle and printed layer is too big. I uses Prusa mendel i3, first layer 0.35mm and other layers 0.1mm, temp = 245C, bed temp = 60C. What is the reason for this problem and how to fix it?
Thank you.

Have you made sure that your steps per mm are correct for your Z direction? ie if you move up 100 mm, does the head actually move 100 mm further away from the build plate?

Also ensure that your extrusion width is wider than your nozzle diameter. For a 0.4mm nozzle, try 0.45-0.6mm.

Did you calibrate the machine?
Always hard to give advise with not enough info to go on...