What issue can cause vertical or horizontal lines in printouts?

The presence of vertical or horizontal lines in printouts is commonly associated with dirty feed rollers. Feed rollers are responsible for guiding paper through the printer. When these rollers become dirty, they can fail to grip the paper evenly or consistently, which leads to imperfect alignment during the printing process. This inconsistency can manifest as lines or streaks in the output, disrupting the overall quality of the print.

In contrast, a malfunctioning fuser primarily affects how the toner is adhered to the paper; it may cause issues like smudging or ghosting rather than distinct lines. A clogged printer head, particularly in inkjet printers, usually results in missing colors or gaps in printed images rather than linear defects across the page. Finally, using an incorrect paper size typically results in misalignment during printing or may cause paper jams rather than producing lines on the printed materials. Thus, dirty feed rollers are the specific issue that directly leads to vertical or horizontal lines appearing on printouts.