Within the HP 5000 5500 Designjet printers and other designjets with tube systems, they can get air in the tube system from fault on the ink cartridge or worn tube system, where the ink cartridge and printheads are inserted. To recover from faulty ink cartridge: replace ink cartridge to prevent it happening again, need to draw ink out of the tube line using a syringe then replace the printhead as there is no way of getting the air out of printhead.
Please see Video!
If it is not the ink cartridge, then you do need to replace the tube system which on a HP 5000/5500 Designjet is customer replaceable.
Post time: Feb-01-2019