my HP Officejet 4620 is not printing black since yesterday and prints only in colors
I had the same issue with my hp officejet 4620 not printing black. Running the printer head cleaning worked for me. Now the black ink prints fine.
Perform a clean print heads at levels 1 & 2, align print heads, update the printer software, manually clean the printer head. if the above troubleshooting steps does not help. I would suggest removing the blank ink cartridges, turn the cartridge over and examine the area. If the plastic lump above the surface, it can prevent the cartridge from seating properly. Before replacing the black ink cartridge, try this. Dribble a few drops of hot water into the ink port on the cartridge then place the cartridge back into position