An ink delivery system for an ink-jet pen having a print head with ink nozzles and a cartridge with an internal reservoir divided into a capillary material filled volume and a free standpipe volume. The print head is mounted on the cartridge adjacent the standpipe volume. The ink delivery system further includes a circulation conduit removably connected to the standpipe volume and the capillary material filled volume to permit fluid flow from the standpipe volume to the capillary material filled volume. A supply conduit connects an ink supply to the circulation conduit. A pump connected to the circulation conduit pumps ink from the ink supply through the circulation conduit to the capillary material filled volume. The pump further operates to pump fluid from the standpipe volume through the circulation conduit and to the capillary material-filled volume thereby filling the cartridge with ink, removing gas bubbles from the cartridge, priming the print head nozzles, and dissipating heat generated by the print head.