I have a HP CP1215 and a HP CP1518ni. Both have developed a similar problem, though with the CP1215 the problem has gone to the point of being unable to print.
After printing one sheet, the printer is unable to grasp a second sheet and pull it through the system. Sometimes it will just not pick up the sheet at all, and other times it will grab two pages, with a pause between the two pages. In either case, the printer diagnoses this as a paper jam (whether there is actually a sheet partially fed or not, and so everything has to be opened up.
I cannot see the paper feed rollers to see if there is some kind of build-up or deterioration on these. With the CP1215, I cannot get it to grasp a sheet at all, either from the tray or the bypass.
This problem seems to be present for all paper weights and regardless of smoothness. I want to either repair myself or find someone who can repair it.