Thin lines running the length of every scan, or a gray smudge in the same spot on each page, nearly always come from something on the glass the scanner reads through. The trick is knowing which glass: feeder pages pass over a narrow strip that's easy to overlook, while the large flatbed glass handles books and single sheets. This guide shows how to find the culprit, clean it safely, and what to check if the line survives.
What you might be seeing
- A thin line runs the full length of every page
- Lines appear only when using the document feeder
- A gray band or spot sits in the same place on every scan
- Copies and scans both show the same mark
Common causes
- Dirty feeder scan strip
- Feeder pages move past a fixed point on a narrow glass strip, so one speck of correction fluid or toner becomes a line down the whole page.
- Smudged flatbed or lid backing
- Fingerprints and dust on the main glass or the white pad under the lid show up as spots or haze.
- Marks on originals or image processing
- Some lines are printed on the originals, and heavy sharpening or magazine dot patterns can create streaks.
- Calibration drift or sensor wear
- If cleaning changes nothing, the scanner may need recalibrating, or its sensor or light source may be failing.
How to fix it, step by step
Work through these in order and test a print after each one. Most people are done within the first few steps.
Turn the printer off before cleaning, and never use pointed tools, solvents or sprays directly on the scanner glass.
Find out which glass is causing it
Scan the same page once on the flatbed glass and once through the document feeder. If the line appears only in the feeder scan, concentrate on the narrow feeder strip. If it appears in both, start with the flatbed and lid. A line in exactly the same position on every page points to the glass, while one that wanders usually comes from the originals.
Clean the narrow feeder strip
Turn the printer off. Lift the lid and find the long, thin strip of glass beside the main glass, usually on the left. Wipe along it with a lint-free cloth lightly dampened with water or mild ammonia-free glass cleaner, never spraying the glass directly. Viewed at an angle under a light, dried correction fluid or glue shows as a raised spot; rub it off through the cloth with a fingernail, never with metal.
Wipe the white guide above the strip
On the underside of the feeder, directly over the narrow glass, is a white plastic strip or roller that pages slide across. Dirt there causes lines too and is often missed. Wipe it with the same damp cloth, then dry the glass and the white guide fully before closing the lid, since moisture leaves its own streaks.
Clean the flatbed glass and lid pad
Wipe the large glass with a barely damp lint-free cloth in straight overlapping passes, then buff it dry with a second cloth. Clean the white pad under the lid the same way, since the scanner sees it around the edges of smaller originals. Skip paper towels, which shed lint, and abrasive or ammonia-based cleaners, which can damage the coatings on some scanner glass.
Rule out the originals and scan settings
Hold an original up to the light to see whether the line is printed on it, which is common on pages that were faxed or copied before. If it's clean, reduce or turn off sharpening and edge enhancement in your scan software. For glossy magazines and brochures, switch on Descreen if your software offers it; it removes the fine dot pattern that can resemble streaks.
Let the scanner recalibrate
Many scanners calibrate at start-up against a white reference strip, often under the edge of the glass frame. Wipe that strip if it's visible, then restart the printer. If the maintenance menu or the manufacturer's app has a scanner calibration or shading correction option, run it with the lid closed and the glass empty, then scan a test page.
Separate scanning from printing
If lines appear on copies but not on scans saved to the computer, the scanner is fine and the fault is on the printing side, such as a clogged printhead or a marked laser drum. If saved scans still show the line after thorough cleaning and calibration, the scan sensor or its light source may be worn and needs service rather than home repair.
How to keep it from happening again
- Let correction fluid, glue and fresh ink dry before scanning
- Remove staples, clips and sticky notes before using the feeder
- Wipe the feeder strip weekly in busy offices
- Keep the lid closed when the scanner isn't in use
Common questions
Why do lines show up only when I use the document feeder?
In the feeder, the sensor stays still while the paper moves past it, so one speck on the narrow strip is read on every line, drawing a streak down the page. On the flatbed the sensor moves under a still page, so the same speck shows up as a single dot.
Can I use ordinary glass cleaner on the scanner?
A little mild, ammonia-free glass cleaner on a lint-free cloth suits most scanners. Spray the cloth, never the glass, because liquid can seep under the edge and dry on the inside surface, where only a service visit can reach it.
The line is red, green or blue rather than gray. Does that matter?
Usually it still means dust on the glass. Color scanners read each color through a separate row of sensors, so a tiny particle can block just one of them. Clean the glass first; if a colored line survives cleaning and calibration, the sensor may need service.
This guide is general information written for common home and office printers. Menus and button names vary between models, so check your printer’s manual where a step differs. Printer Problems Solved is independent and not affiliated with any printer manufacturer. See our disclaimer.