I've had my Z3100 since the end of May. Everything has been working fine except in the last few weeks this problem has arrisen.
I'm getting drips of black ink falling from the print head onto the paper intermittently when printing. In the worst case I'll get ink in several places on the leading edge of the paper about 1/2 inch from the edge. This doesn't happen very often. More frequently, I'll get a few lines of ink only on the left side of the paper (as you face the back of the printer) starting about 1 inch from the leading edge. Then, no ink drips for the rest of the print. I can print several large prints without any ink drips, then 1 or 2 prints will have them. The drips never occur within the image area, only on the extreme left side and occasionally on the leading edge of the print. I watched the printhead going back and forth through the window with a flashlight while the printer was printing, and can identify which part of the printhead is dripping ink. It comes from the part of the printhead closest to the front of the printer. In other words, observing the printhead assembly, I can see the ink being laid down after the assembly makes a pass, putting a line of ink on the paper where previously there was none.
I pulled out the heads a found them to be clean except for the Red-Matte Black head, which had a lot of black ink deposited on the sides and front and back of the head. There also was some ink on the contacts on the head as well as on the contacts on the printhead assembly. There also was black ink on the bar on the printhead assembly on which the printhead rests. I cleaned everything, put the head back in, and the printer did a head alignment. This seemed to solve the problem for awhile, but returned later. Taking the head out again, I noticed it had accumulated some ink, so I cleaned it again. Problem solved for awhile, but returned again.
Note that I'm printing on glossy paper, so I'm not using any matte black ink. But it's black ink on the Red-Matte Black printhead that's accumulating.
I called HP and explained the problem. They sent me a new Red-Matte Black printhead, but that did not solve the problem. In addition, before I received the new head, my Matte Black ink ran out even though I've hardly printed on matte papers at all. It was the original 69ml cart. The printer said the cart was empty, even though the ink level indicator in the Color Center said it had 23ml. What this seems to mean is that ink is leaving the matte black ink cart in a way that the printer ink monitor can't see, i.e. dripping out, rather than printing out through the nozzles in the normal way.
I called HP today and explained that the replacement head was having the same problem. They are going to send a service person out either Friday or Monday.
Another thing I noticed. While the head assembly was parked in the head changing position, I took a flashlight to look inside the right side of the printer where the head assembly normally is parked. I saw what seemed like a lot of ink on the waste ink pad (color ink on the left part of the pad and black ink on the right part of the pad). Also there is something just to the left of the waste ink pads which seemed to have a lot of black ink on it. I don't know if this is normal, or could it be part of the problem.
Does anyone know how ink gets from the nozzles of the printhead to the front, back and sides and even onto the contacts of the printhead?
One last thing. HP's service has been great on the 2 phone calls I had with them.
Tomorrow, I'll try to post some pictures of the ink marks.