HP OJ 8210 Printhead

[MATT-C-L]

I'm trying to find out how long printheads usually last? I've got a HP 8210 and I've started to get smudging prints. I've tried to clean the print head but doesn't make any difference. Do they have estimated life spans? I thought they might be a bit like drums in brother printers where they have a number of thousand page yield.