When printing solid blocks of colour I'm getting a darker horizontal line every 3.2cm

[greyhoundbloke]

I am printing on my HP Officejet 8720. I have tried cleaning the heads and running the diagnostics and everything looks fine until I come to print out solid blocks of colour. I've tried this from two different applications - Excel and Serif Pageplus.

I get exactly the same symptoms. The block of colour has a darker line of the same colour every 3.2cm repeating down the page (in portrait, across the page in landscape). 

[Valsimot · Accepted solution]

Increase print quality from Normal to Best

[greyhoundbloke]

That fixed it. Thank you so much.