Refusing to fix/replace printer

<p>Good day,</p> <p> </p> <p>I have a lemark pro 7000 series all in one printer which is still in warranty. Printer is not printing correctly (printing and missing lines). I called the call center and the agent avised to replace the black catridge. Why would need to replace the black catridge when it is doing this for even color prints ??? The agent is now insisting that I replace the black catridge 1st.</p> <p> </p>