Single PiezoFlush cart not printing on 9900

I have installed rechargeable cartridges filled with PiezoFlush in my Epson 9900. I wanted to clear a problem in the black print head, and the PiezoFlush took care of it. All the heads were printing beautifully and I let the printer sit for a few days. I came back and found that the orange cartridge won’t print.

Cleaning cycles, both regular and power, have not had an effect, though I did initially get a few lines to show on the test page. I have taken it out and primed it with the little attachment that came with my cartridges. I’ve done that twice, but it has not helped. I wonder if there’s a problem with air in the line or some other reason the cartridge isn’t delivering PiezoFlush to the head.

I regularly leave the printer with PiezoFlush when I go on vacation, and it seems to work very well, leaving the heads clean and ready to print. I am concerned about leaving it without the orange cartridge functioning.

Should I do an initial charge of all the inks again? Or can I check the flow from the cartridge to the head and remedy it if there’s a problem?

UPDATE: The cartridge isn’t the problem. I swapped it with another orange PiezoFlush cartridge that I knew to be working on a different printer. The swapped-in cart doesn’t solve the problem. The swapped-out cart prints on the other printer, so I conclude that it’s fine.