I have an old Canon i860 and had an issue with black streaks down the border of my photos. In order to fix this I had to remove and clean the print head. An amazingly easy and quick process.
1. Remove the five ink cartridges.
2. Lift the gray handle on the right side of the Carrier (that holds the ink carts. and the print head).
3. Gently press the sides of the print head toward the middle about a mm, lift a bit and pull out.
4. Set the bottom of the print head on a folded damp paper towel. (Dampen ONLY with warm water)
5. Let set for a couple of minutes. Move to a clean spot and let set again. (I did this four or five times).
6. VOILA! Clean print head.
(With the problem I had it turned out that fibers from some cheap paper had gotten caught in the leading edge of the print head and were just soaking up black ink and then trailing along the photos.)
CAUTION: I was warned to never never use any cleaning solution on this print head.
Hope you find this information useful. Print on, Garth!
greendragonfly advice applies to many other Canon models especially Ip4000 and IP5000 series.
Epson print heads are not removable, especially on the model that I had, they too can be cleaned manually but....
... you have to remove the power plug during the switch on cleaning cycle or print mode as to release the head from the docking bay, folding the paper towel in a thin narrow strip, moisten with warm water then lay the moist strip flat on the bottom and manually move the head over the strip a couple of times, repeating with a clean strip if required and then dried using a dry strip, the print head will reset when the power cord is plugged back in.
Canon i860 Print Head Removal & Cleaning 
Linear Mode
