My window-cleaning robot leaves a streak in the centre of the glass every pass
Home Nura guide — category Window Cleaning Robots
Diagnosis
A streak down the middle of the glass is almost always caused by a dirty cleaning pad or by grime collecting along the robot's centre line. The robot drags dust inwards and then smears it back and forth on every pass instead of pushing it out to the edges.
Possible causes
- Pad saturated with dirt — it wipes poorly at the robot's centre, where pressure is highest, and leaves a dark band behind.
- Pad fitted loosely or creased — a fold leaves a sharp line that repeats in exactly the same spot on every pass.
- Very dusty glass to begin with — the robot gathers the dirt into a central ridge and keeps running over it without absorbing it.
- Too little cleaning liquid — the pad dries out mid-run and rubs the dirt around instead of dissolving it.
Recommended procedure
- 1Switch off and unplug the robot, remove the pad and hand-wash it in warm soapy water without fabric softener, then let it dry fully before reuse.
- 2Check the pad is stretched tight and flat across its full width, following the fitting diagram in the manual.
- 3Wipe the edges and frame of the window with a damp cloth first, so dust and grit are not carried into the middle by the robot.
- 4Spray the manufacturer's recommended cleaner evenly over the pad or glass, without soaking it, so the robot can still grip properly.
- 5Run a second cycle in the criss-cross cleaning pattern, then clean the drive track and the suction seal with a damp cotton bud.
Repair or replace?
If the pad is worn out and the streak stays after a thorough clean, the pad needs replacing, not the robot. Only replace the robot if suction keeps weakening or the tracks slip, because a repair usually costs more than buying a new one.
Other common failures on this category
These incidents affect the same type of appliance — diagnosis and recommended procedure for each.
- Window Cleaning RobotsMy window-cleaning robot keeps losing grip and nearly falls
- Window Cleaning RobotsMy window-cleaning robot leaves streaks after every pass
- Window Cleaning RobotsMy window-cleaning robot beeps non-stop and reports low suction
- Window Cleaning RobotsThe suction pad on my window-cleaning robot is losing grip and the unit slides
Frequently asked questions
In Europe, any window cleaning robots bought new from an official reseller benefits from a legal conformity guarantee of at least two years (Directive (EU) 2019/771). This guarantee covers defects present at delivery, whenever they first manifest.
You can pick: European law puts the legal guarantee on the seller, not the manufacturer. In practice, a store return is usually faster, but the manufacturer can repair if the damage is out of warranty. Keep proof of purchase.
Our public methodology adds a Nura Score /10 penalty to any window cleaning robots whose recurring failures are documented in European user feedback. A model that breaks too often never tops our charts, brand notwithstanding.
Yes, within the limits of the European "right to repair": routine maintenance tasks (cleaning, gasket replacement, calibration) never void the legal warranty. Only irreversible hardware modifications can be a problem. For a window cleaning robots, any handling documented in the manufacturer's manual stays covered.
The directive imposes a two-year legal conformity guarantee, with a presumption of pre-existing defect during the first twelve months — the burden of proof is on the seller. For a window cleaning robots that breaks in that window, you're entitled to free repair or replacement, no strings attached on typical use.