This occurs due to multiple reasons.
Material feeder on the back of the Ultimaker 2 is ticking while printing. Nozzle is blocked or partially blocked by dirt or burned material.
Solution: Increase the print temperature to 260C while printing in an attempt to clear the blockage. If the blockage is removed keep printing at 260C for atleast 10 minutes to clean out any residue.
Printing at 260C doesn’t solve the blockage
Solution: Something larger than 0.4mm could be blocking the nozzle. Cleaning the nozzle or replacing the nozzle is highly recommended. Contact support at firstname.lastname@example.org who will assist in fixing your Ultimaker 2.
Posted in: Ultimaker