Extrusion problems can occur in different ways and can have several reasons. The nozzle could simply be completely blocked, through which no material is coming out of the nozzle at all. But it could also mean that the Ultimaker 2 just doesn’t extrude enough plastic, leading to very thin or missing layers in a print. This is what is called “under extrusion”.
In most cases, extrusion problems are caused by some dirt or carbonized material in the nozzle or another hot end part through which a (partial) blockage is created. In order to get rid of this a few things can be done.
There are some symptoms at the feeder that could indicate an extrusion problem. These are however often a result of a problem in the hot end, rather than the cause of the extrusion problems. You may for example notice a ticking sound at the feeder or see that the filament has grinded, which means that the knurled wheel of the feeder has dug in the filament through which it has flattened. In the latter case it is important to remove the grinded filament from the Ultimaker 2 and load a new piece of filament.
Furthermore it is important that the tension on the feeder is as loose as possible. Therefore make sure that the white insert clip is completely at the top.
The Ultimaker 2 offers the possibility to manually extrude some material. Therefore you have to go to Maintenance > Advanced > Move material. Wait for the nozzle to heat up and rotate the button to forward the material. You can put some extra force on it by manually pushing the material below the feeder while doing this. If you manage to get some material through the nozzle while it was completely blocked before, it means that the blockage has been cleared. In that case you can simply start a new print.
If there is just some dirt or carbonized material in the nozzle or another hot end part, it’s important to clean it. Therefore it is recommended to use the Atomic Method, which is a simple though very effective way of cleaning the hot end. Especially if the dirt in the hot end is bigger than the nozzle diameter, the only way to get it out is from the top.
We also advise to use the Atomic Method when switching from a material that needs a high nozzle temperature to a material that needs a lower nozzle temperature, for example when switching from ABS to PLA. There may still be some residue of the previous material in the nozzle and it is important to get this out first.
After having used the Ultimaker 2 for a longer time already it could also mean that the PTFE coupler has deformed, causing friction to the filament. This consumable item has the tendency to wear over time due to the heat and pressure from the hot end. If none of the above described options works, it is advised to take a closer look at the PTFE coupler. A deformed PTFE coupler can be recognized by a (small) brim on the inside at the bottom. The below image clearly shows the difference between a new (left) and used (right) PTFE coupler.