Hello Andy,
I searched the Support page and found this article for colored lines that may help you resolve your issue.
I have had this printer since 1st of June and after finding a method of printing from the by-pass tray (which was not in the manual), I have had a problem with two pink lines appearing about a third of the way down on every coloured print. This is only a problem when colour printing as B&W prints are fine.
I have followed the recomended solution using the step by step cleaning instructions in the manual, but with no success. I have only had the printer for 10 days and it was not used for five of those days due to holliday. Any Ideas before I return the printer?