How to Clean a Canon Printhead
Over time, ink can build up and then dry out on the printhead of a Canon, and quality begins to suffer, even if you remove and replace the ink cartridge. If this happens, the printhead needs to be cleaned. The printer can clean itself, and all you need to do is press a few buttons. But if the buildup is too severe, you'll need to clean the printhead by hand.
Navigate to your printer's control panel through the Start menu. Depending on the printer model and age, there might be self-cleaning commands there. If not, consult the manual for how to key a self-cleaning command directly into the printer.
Execute the self-cleaning command. Follow this up by printing out a new document, or have the machine produce its standard test page. If the quality problems remain, you'll have to clean the head by hand.
Consult the printer's manual and locate the printhead. You'll probably have to remove the ink cartridge to get to it.
Remove the ink cartridge.
Dip a cotton swab into hot water. Rub the swab against the printhead gently. This should remove the ink buildup.
Remove the print head if the problem persists, and soak it in isopropyl alcohol for a night. In the morning, carefully dry it off and reinstall it.
Print a test document. If the problem persists, an unclean printhead may not be the root issue.