Printer sometimes doesn't print

Solution 1:

In case it helps anyone, I have these same symptoms (print jobs go to pending and never print) unless my printer is turned on after Ubuntu starts up. Therefore, if I have print jobs pending, turning the printer off and then on again is enough to get them going.

Solution 2:

Running sudo service cups restart will restart the printing software, fixing the problem.

I'm a complete Linux novice, but I somehow I hit upon executing the command and it worked without a hitch (I was given a clue when I ran pgrep hp and it gave me 2 hp processes and one hp-cups process).

Solution 3:

I had this problem but nothing worked. What I did to solve it was go to printers from the dash, right-click my printer and then realised there was no tick next to "enabled". Once I clicked this, it worked again. Something I'd installed must have disabled it for some reason :/