Just had similar issue. Red and yellow were spotty, then the yellow stopped printing altogether as I printed test sheets. This printer (GX7021) is only seven months old, and I use it routinely, so this seemed odd. After multiple cleanings and a deep cleaning, the red slowly came back. The yellow did not. My maintenance cartridge was about half full after the deep cleaning. I waited 24 hours like the manual suggests, but the situation did not improve. At that point, I decided to remove the print head for a manual, out-of-printer cleaning. With the print head removed, I stared at the print head (the "death stare" is a crucial step in any repair). This gave me a moment to notice air bubbles in the yellow ink tube leading to the print head. I do not know whether the air bubbles were the problem, but based on that, I decided to reinstall the print head rather than try to clean it. The reinstallation of the print head involved a helluva racket that went on for about four minutes. It ended with a message that the out-of-stock maintenance cartridge was full and needs to be replaced; however, the yellow started working again.
"Your mileage may vary."
I have a few gentle suggestions for Canon because this printer nearly got shipped back to repair depot today:
1) Please keep the maintenance cartridges in-stock because they are obviously crucial to keeping these printers working;
2) Please provide more detailed troubleshooting suggestions in the user manual, including a discussion of whether the air bubbles I saw are a problem, and if such can be cured by some user maintenance procedure that does not involve excessively using up maintenance cartridges and ink;
3) I have been printing nozzle test sheets every few days to keep the colors flowing, but it would be good to know if printing such small quantities of color is good or bad, or might even cause the bubbles I saw, or otherwise be a poor method to keep the colors from drying out. Maybe there should be more nozzle test patterns or user exercise routines that focus on just the colors (black is not likely to dry out) or on one color at a time.
I have previously cleaned a PIXMA print head out of the printer several times. It is not a pleasant process that can take up to a day. I feel like there is some information or suggestions missing from the documentation that could help the users better prevent these printers from clogging up.
