I've been using your inks and carts for some time (year and a half?), with only one minor problem until last week. The minor problem was that the printer would tell me it didn't recognize the photo black and matte black carts (the former yours, the latter Epson) upon start-up. I would just take the carts out and put them back again, problem solved.
Last week it suddenly stopped printing black -- fine in the morning, gone in the afternoon. The cart was nearly empty but there still seemed to be a bit left in the exit chamber. I refilled using vacuum method, then ran a head clean, but the nozzle check gave only a few bits of PK, maybe 5% of a full grid (all the colors printed fine). I ran another head clean and got even less, one or two patches. I then tried switching to matte black, but also got nothing. (I'm afraid it has been some time since I used matte black.)
Looking at info on your website, I decided to try cleaning the capping station. I haven't done this before (should have read your maintenance instructions), but it didn't look bad. The printer gets light, somewhat irregular use, but I try to at least print a few things every couple of weeks so it won't dry out, and I shake the carts once in awhile. I did clean the capping station with distilled water, but this made no difference. Cleaning the print head seems a riskier procedure so I haven't tried that.
Now I'm wondering what to do. Does my account allow you to draw conclusions that I don't have the experience to draw? Should I assume it's a cartridge problem, since it happened so suddenly, and buy a new one? Is there anything more I can do to test potential causes? I have looked at some threads on this forum that seemed relevant, but I'm afraid I don't know enough of the lingo being used to make all that much sense of those discussions.
Any help would be much appreciated.