Printer has stopped printing black

Question

I have had my printer for about 3 1/2 years now and it has always worked fine. However, recently it suddenly stopped printing black. I noticed that the ink was low so I replaced the cartridges (on all 4 colours) using original HP cartridges but this has not solved the problem. I tried cleaning the print heads more than once without result. The printer software on my laptop reports nothing amiss with the ink monitor showing all colours full, nor is there any fault showing on the printer's display. All the test pages that I have printed print the three other colours fine but wherever there is supposed to be black, there is nothing. All-text pages are completely blank and colour pages show only coloured text. As long as this problem persists the printer is unuseable.

Answer 1

I've had a similar experience and outcome with my printer as described @ Londonitalian, although I've owned my printer 4 or 5 years.  My printer is the Officejet 6500 e709n AIO (my first AIO) and up to now it worked well for the most part, minus a few hiccups here and there, including a large appetite for ink and a high rattling / struggling noise level, but I was always able to correct issues that popped up.....
My serious problem began on 1/4/15 and after days of exhaustive troubleshooting exercises (testing , retesting, re-installing drivers via CD and HP website and applying updates, unplugging, replugging and multiple printer reboots / resets and alignments, etc., etc.), I concluded that the new HP ink cartridges that I had just put in were defective (anything is possible these days and what do I know), especially since one of the reports showed color ink level had dropped nearly 30% upon replacement, whereas the black ink did not show up but remained at 100% on the ink level monitor, and no printing other than test exercises had been done.  Also, all diagnostic tools indicated like yours that all was well with the printer.
So, I took the newly opened HP ink combo set (packaging and all) back to Staples and exchanged for a new set. (Fortunately, the purchase receipt was still in the bag with the ink in the file cabinet as I had purchased it last July as a back-up set and put it away - checked ink date and was not expired).  I also found instructions online on how to remove and clean the printhead for my printer, which I followed very carefully and was beginning to feel very good about my adventures (as a 60+ year old female)!  After cleaning with water only and drying the printhead as instructed, I put in the new HP ink cartridges (ones exchanged by Staples) and began to get error messages that I had not experienced before; addressed them all and finally the ink levels were appearing again on the monitor.  But still the printer would not print and the test results were the same...blank sheets and no black ink.
Again, I disassembled everything and with the aid of a flashlight, I looked far into the printer and noticed large clogs of black gooey stuff, as if something had spilled over, in front of the docking area (far right hand side of the printer where the moveable mount and printhead reside when not in use), which is not an area easy to see or access.  I took a pencil and removed gingerly as much gunk (turned out to be all ink) as I could reach.  Then I did a second cleaning of the printhead as before and let it dry even longer. 
I re-assembled the prinhead and installed the cartridges into the cradle, and still no printing but got new messages stating that the color ink cartridges were low and needed to be replaced!  As before the "first cleaning fix" and all troubleshooting, print status reports showed color ink but no black ink and by this "second cleaning fix" the color ink was very low and the black ink remained non-existent. And, moreover, from the start of this problem to now, the only print jobs that have come out of this printer have been diagnostic troubleshooting exercises, which I now know use an excessive amount of color ink  to produce no solution!
Now I don't know if the marketplace or even HP provides "inexpensive testing cartridges" for consumers troubleshooting purposes but they should.  But what I do know is that at $60+ for original HP ink set, I will not be purchasing a new ink set to determine or troubleshoot if my second cleaning of the printhead was a success or not. After some experimentation, it appears as though the program code on this printer, even during troubleshooting, is written for all ink levels to be at a very high level, whether ink flows through or not!
However, before ditching all efforts, just in case my printer problem was above my "pay grade", I called a repair company, listed as an authorized HP service company, about bringing the printer in for an evaluation. After all, I like the printer/features and had gotten it at a decent price on a Saturday following Black Friday at Staples, although by now I've paid several times over in ink replacement cost alone!   Also, the printer has not been heavily used and still looks fairly new.  I spoke with a gentleman at the repair service company and was advised that I would probably be better off buying a new printer as labor and parts for an inkjet printer would be more expensive than the cost of purchasing a new one!
Londonitalian, I hope you have better luck in finding a solution to your problem but I am now shopping for a new printer and hopefully, I will find a quality one that utilizes ink efficiently and has a low replacement cost for ink cartridges.  My HP Officejet 6500 e709n AIO has let me down and I've spent far too much time trying to find a solution to its current ailment, blank page and no black ink.
After nearly 15 years and three HP printers, I'm inclined to broaden my printer brand search.....