Ultimaker 2+

Leveling the Build Plate
This will be more common. Essentially, the build plate must be level relative to the X and Y linear axis rods of the machine. Additionally, the build plate must be a consistent and precise distance from the nozzle at all points.

There are three screws on springs under the build plate, one on the front left, one on the front right, and one on the back of the plate. Tightening one of these screws tightens that spring, and brings that are of the build plate lower relative to the head.

If the print head is too far away from the build plate, then the filament will solidify before reaching the plate, and not stick. If the print head is too close, the pressure will prevent the filament from extruding properly, and it will either come out too thin, or not at all.

To do a full re-level, start by tightening all three screws by at least three turns. Then go through the menu to Settings -> Build plate. It will walk you through leveling the plate in full.

To do a fine re-level, which is faster (and should be done after a full re-level), start a print (preferably with a large print area). Then as the lines go down, slowly adjust the screws until the layer looks consistent and clean.

Fixing the Feeder
The feeder should VERY RARELY need adjustment. However, if the feeder arm is not tensioned well, the tooth gear grind up filament, or not push filament at all.

An Allan key turning the screw on the top of the feeder block will tighten or loosen the spring on the feeder arm, and can be seen on an indicator on the side.

If tensioned properly, the tooth gear will leave some marks on the filament.

If not tensioned enough, there will be no marks on the filament.

If tensioned too tightly, it will grind the filament leaving heavy scores.

Unclogging the Nozzle
THIS SHOULD BE RARE. Dust, dirt or fragments of other material can become clogged in the nozzle of 3D printers.

Method 1

Heat the print head to the recommended print temperature of your material (210 for PLA), then manually attempt to (gently) push material through. Sometimes a small amount of additional pressure than the feeder provides can unclog an artifact.

Method 2

A Cold Pull is where you heat the print head up to slightly higher than your print temperature, roughly 230 should be fine. Then insert a strand of your material manually. Lower the print temperature to 90. Once the printer is at this temperature, pull the filament out in one quick, firm motion. The tip of the filament will have melted around dirt, dust, etc. and pulled it out on its way out. You should have a consistent coloured, cone shaped tip. If any dust was pulled out, or the tip is not consistent, perform this again.