I bought an Epsom C64 printer in June and have just replaced the colour cartridges and found that the yellow appeared not to be working. (Tight git I bought non-Epsom refills). I then bought an Epsom branded yellow cartridge to find there is still no yellow being printed, although the user screen shows the ink level (and other ink levels) going down at quite an alarming rate. I have cleaned the nozzles, checked their alignment.
It will soon be cheaper to bin this printer and buy another new one!
But is there any answer to this problem?
Thanks, in advance
Tez

Sounds like the print head is clogged. That's a common problem where third-party refills have been used.

Try this article for ideas. It's written by one of my colleagues.