I have not had this printer very long, but recently the black ink was low. I replaced it with the correct black cartridge that the printer requires, yet it will NOT print black at all.
I returned the ink and bought a new one - and same problem. I have also followed the troubleshooting advice that I have seen given to others with the same problem, but cleaning the printhead and cleaning paper-smear has done nothing to fix the problem. (It wasted plenty of paper and other ink cartridges, however!)
Upon seeing that this appears to be a common issue with the OfficeJet 6978, I checked my warranty which has conveniently expired. (Is the warranty now less than a year?!)
I am quite upset that the printer is less than 2 years old and is already nothing but an expensive paperweight with fresh, new ink. I had purchased this printer to replace an older HP printer that was having problems -- only now I wish I had gone with any other brand!
I think it's TERRIBLE that this appears to be a known issue and yet the only way to resolve it is to send it in and pay for something that is the manufacturers fault. If this cannot be fixed, I am never buying another HP product again.