Wow, our printers must be linked or something, we had the same problem with one of our white heads earlier this week. Inside of the cup above the head where the ink fills, there is a small "Thermistor" I think they call it. If there is a build up of ink on said thermistor, the head thinks it has ink in it, even though it doesn't. Take the cap off that cup (they are grey on our machine and they are numbered 1-6) 4 phillips head screws, one in each corner, be careful because there is an o-ring on the seal that is very important. If that little glass rod is covered with ink, VERY CAREFULLY wipe it off with a lint free cloth and head flush. Be very careful because it is glass and if it breaks you are SOL. Clean the thermistor, put it all back together, fill that head with ink, then do a few purges. I literally just did this on Wednesday because our #5 white head was not printing at all when i did a jet test.