I replaced all the cartridges in this printer and all the colours printed fine and they were recognised by the software. The black was not printing properly so I cleaned the head 4 or 5 times and it did not improve. I took all the cartridges out so I could inspect it to see if anything obvious had gone wrong. When I put them in they were all not recognised. I see from reading various posts that there is a sensor on the fixed part of the print head, and it seems you can get air in which renders the machine permanently useless. Any suggestions gratefully received.