Hp officejet 4215 all-in-one. 2

hp officejet 4215 all-in-one. 2 yrs old, rarely used.
prints first page perfectly but subsequent pages are streaked as if ink is running out. Have checked ink levels which are showing half full. Self test report ok apart from one white streak on black bar. Clean print cartridge - loads of streaks on black bar, streaks on blue bar also.
Info at top of latter test is gobbledegook. Help me, before I throw it out of the window!