Sorry for the long post ... sort of a summar of my experiences. If you want to get to the main point of my post, you can skip down to the bold subtitle.
There have been quite a few posts about the issues with 7900 printers and excessive nozzle clogs, resulting in very high consumption of ink to clear nozzles. As a very satisfied owner of an Epson 11880 which has been virtually clog free, the 7900 has been a great disappointment in this regard. While the print quality to me exceeds all other devices, the enormous amount of ink this printer has consumed makes it completely unusable. To Epson's credit they have been very aggressive in trying to resolve this, including replacement of nearly every part in the printer multiple times, and finally at my insistence replacing the entire printer. In addition, they have provided more than adequate ink to compensate so the only thing I have invested is the time I have spent trying to understand the issues and hopefully resolve them.
Unfortunately I am not alone in these issues, and some of these printers appear to have a serious flaw. I have called a couple of people that have disabled the Auto Nozzle Check and believed this has solved their problems, but judging by the consumption of their waste cartridge, it has not. The printer is still using far more ink to keep nozzles clear than it should.
As I mentioned, my comparison has been the 11880. In the 18 months I have operated this machine, I use it very sporadically. I often go weeks without printing anything at all, sometimes I print several days in a row. I have accidently left the printer on a few times for several days, but most of the time it is off. The Auto Ink Detect circuitry in this printer seems to be unreliable, and was switched off when I found the printer cleaning frequently despite perfect nozzle patterns. Since disabling ANC, I have cleaned the 11880 less than 10 times, and it may even be less than 5. I can only recall cleaning it a handful of times, and without ANC on, it doesn't clean on it's own.
I just received a replacement 7900. While it is a little early to say (some users say their printers "settle" down after a while), I have already had to clean this printer 4 times in 8 days. I am no longer calling these nozzle clogs, but nozzle failures, because they sometimes are not typical of other Epson printers clog problems I have had . I have been logging every action, print, and nozzle check on this printer. Each day after starting the printer I print a nozzle pattern, and each night I print one. On two occasions a morning nozzle check showed multiple problems despite perfect nozzle checks the evening before. This included massive amounts of failed nozzles in several colors (at least 40% or more). I can't imagine how much ink on the head it would take to "clog" this badly- I never saw this even on my 9600/4800/4880 printers except perhaps when they were left off for very extended periods of time. Maybe ink is leaking out of the nozzles and drys while it sits idle. Another thought is the ink delivery system is losing pressure and the nozzle isn't actually clogged .. there just isn't any ink there. Some have speculated air in the lines which eventually settles out, but even power cleans which should have purged the lines failed to solve the problems. There have been enough problems with these printers that I am assuming Epson is aware and aggressively trying to isolate the problem.
In reality there are two main issues. One is the inaccuracy of the Auto Ink Detect system .. it seems nearly every user has disabled this feature because it just doesn't work ... it continues to trigger cleaning cycles despite nozzle checks that show no issues. Once a cleaning cycle has started, ANC will be performed whether you have disabled it or not and if the AID (auto ink detect) unit is defective it will continue to clean a predetermined number of times until finally alerting you cleaning has failed and asks if you want to clean again. Declining that option and printing a nozzle check has always confirmed the nozzles were all functioning.
I have had 4 head clog issues with this new printer. The first was after the initial fill ... a couple of nozzles in the PK channel didn't show up. I had the machine clean just the one color pair, which seemed to work as expected, using @1ml of ink in the two colors. Everything was great for 3 days. On the 4th day a morning nozzle check showed problems with 4 colors, including the green missing at least 30% in the middle. I had the printer perform a single channel clean of the orange/green channel. It took 25 minutes, and consumed at least 7% of every color of ink, a total of @80ml. When completed all colors were clear. Discouraging to say the least - that's about $30 worth of ink.
Now for the main point of my post...
Again things went good for a couple of days until I came in on Monday. 8 colors had missing nozzles, including 4 with 20% or more missing. Rather than simply run the standard cleaning cycle, I decided to try to discover if cleaning in service mode used ANC. There are a great variety of cleaning options in service mode, including 4 different levels of cleaning for either the entire head or for individual channels. I had the machine perform a CL1 (the least aggressive clean) on just the PK/LK channel. When it was complete, those colors were clear on a nozzle check, the other colors remained unchanged. The printer did not perform the ANC and try and clean the remaining colors like it does when using the normal clean. In addition, it used only @1 to 1.5ml of ink per color. I went back into service mode and formed a CL1 on the entire head. Afterwards the entire head was clear, and consumed only @10-15ml of ink.
If your ANC circuitry is working well this may be all of the ink that is consumed as well, although it appears to me the normal mode cleans are more aggressive than the CL1 from the service mode.
Whatever the underlying problem with the printer is, it appears it does not need aggressive cleaning to restore nozzles, and if you bypass the ANC system using service menu cleans, you may be able to reduce ink consumption down to at least a somewhat tolerable level. While I do not like having to clean the printer when starting it up most of the time, at least now I can now do so using far less ink.
I'm not sure of Epson's policies regarding starting the printer in service mode by an end user, and I know there are things in there that you can do that might mess up the printer. I have been asked to do it by Epson on numerous occasions so I'm very familiar with how to do it, but I am uncomfortable posting the method in case it some how invalidates warranties or the like. I would encourage all of those who get frequent clogs on these printers to contact service and tell them you would like to use the less aggressive and ANC free service mode cleans to save ink.
Again, if you think turning off ANC has eliminated your problem, I would recommend you look at your maintenance tank life. My new 7900 is already at 60%, my previous printer as at 40% of it's 2nd tank, and my 18 month old 11880 is still at 40% of it's first one.