Litter Robot 4 not cycling: causes and fixes
A litter robot 4 not cycling is usually waiting on its timer, in Sleep Mode, blocked by dirty curtain sensors, or reading extra weight on its scale. Here are the causes and fixes from Whisker's support site, matched to the light you see.
Researched by Riley Hart · updated Oct 15, 2026 · How we research
Check the light bar first. Solid red means it is counting down its cycle delay (7 minutes by default), solid purple means Sleep Mode, red and blue alternating means dirty curtain sensors, flashing blue means the drawer is full, and blue with 2 flashing yellow means the scale reads extra weight. Fix the cause, then press Reset and Cycle.
| Light bar | Likely cause | Fix from Whisker |
|---|---|---|
| Solid red | Cat sensor triggered, delay countdown running | Wait for the delay to end, or short press Reset to cancel the countdown. |
| Solid purple | Sleep Mode (8 hours a day by default) | Long press Cycle for 3 seconds, or change the schedule in the app. |
| Red and blue alternating | Dirty curtain sensors | Wipe the bezel with a dry cloth and vacuum its inside edge. |
| Flashing blue | Drawer full | Empty the drawer, press Reset, then Cycle. |
| Blue with 2 flashing yellow | Scale triggered over 30 minutes | Remove litter above the fill line, fix placement, zero the scale. |
| Solid yellow | Paused | Press Cycle or Reset. If needed, power off and on. |
| Flashing yellow | Bonnet removed | Reinstall the bonnet. It resumes after 5 seconds. |
| Blue and white alternating | Motor connection fault | Reseat the motor per Whisker's motor installation guide. |
| No lights | No power | Check the 15V DC 2A power supply, outlet and barrel connector. |
From Whisker's Litter-Robot 4 not cycling, light codes, no power and sensor support articles, checked October 15, 2026.
If the same code comes back after the fix, contact Whisker support first, especially under warranty. Out of warranty, compare the repair quote with a new robot's price and 3 year cost.
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We read every question. When several owners ask the same thing, the answer goes on this page.
1. It is waiting on the cycle delay
After a cat leaves, the Litter-Robot 4 waits before it cleans. The default wait is 7 minutes, and the light bar shows solid red while the cat sensor is triggered. Whisker says the unit cycles when the countdown ends or when you press Reset on the robot or in the app Controls.
You can set the wait anywhere from 3 to 30 minutes. If it seems slow, it may simply be set to a long delay.
2. Sleep Mode is on
Solid purple means Sleep Mode. The default sleep period is 8 hours, repeating every 24 hours. No Clean cycle runs during sleep, but a visit during sleep triggers a cycle after the unit wakes.
Long press Cycle for 3 seconds to turn Sleep Mode off. In the Whisker app, go to your device, tap Controls, then Sleep Mode, and pick a schedule. Weekday and weekend schedules are supported.
3. The curtain sensors are dirty
Three laser curtain sensors in the bezel check for a cat and the litter level. Dust and fur block them, and the light bar alternates red and blue.
- Wipe the bezel sensor area with a dry, clean cloth.
- Vacuum the inside edge of the bezel with a brush attachment, passing over the holes at the top.
- If the light bar shows green with 2 flashing red, auto calibration failed. Clean again, using a cotton swab if needed, then short press Reset and Cycle. A blue light bar back at Home means it is fixed.
4. The scale thinks a cat is inside
Extra litter, a recent move or bad placement can make the scale read weight when no cat is there. Whisker's minimum cat weight is 3 lbs. Blue with 2 flashing yellow, or flashing red, means weight has been detected for over 30 minutes.
- Remove litter above the fill line.
- Place the unit on a firm, level surface with all four feet moving freely, not on a cord or grout line.
- Keep all sides clear of walls, and put any litter mat fully in front of the unit.
- On carpet, Whisker suggests the Litter-Robot 4 Carpet Tray.
- Zero the scale: from Home, press Reset twice. If it is stuck mid cycle, long press Reset for 3 seconds.
5. The drawer is full
A flashing blue light bar means the drawer full indicator is triggered, and the unit will not keep cycling. Empty the drawer, press Reset, then Cycle. If it flashes blue with an empty drawer, Whisker says to confirm the unit is plugged in, online and running current firmware.
6. Power or motor problems
If there are no lights, check that the power supply label reads 15V DC 2000mA or 2A, test the outlet with a lamp or charger, and push the barrel connector firmly into the back of the base. Then press Power and Cycle.
Blue and white alternating means a motor connection fault. Reseat the motor using Whisker's guide. If the pattern stays, Whisker says the unit likely has a defect. Under the 1 year WhiskerCare warranty, replacement parts ship at no cost; call 1.877.250.7729 for help.
Litter-Robot 4 profile with 3 year cost
Questions people ask
Why won't my Litter-Robot 4 cycle after my cat uses it?
It waits for its cycle delay first, 7 minutes by default and adjustable from 3 to 30 minutes. If the light is purple, Sleep Mode is on. If it alternates red and blue, clean the curtain sensors.
How do I force a Litter-Robot 4 to cycle?
Short press Reset to cancel the countdown, or press Cycle to start a Clean cycle. You can also use Reset in the Whisker app Controls.
How do I reset the Litter-Robot 4 scale?
From the Home position, press Reset twice to zero the scale. If the unit is stuck mid cycle, long press Reset for 3 seconds.
Why does my Litter-Robot 4 think my cat is still inside?
Usually extra litter, carpet, a mat or cord under the feet, or contact with a wall. Remove litter above the fill line, move it to a firm level spot and zero the scale.
Does the Litter-Robot 4 cycle during Sleep Mode?
No. It skips Clean cycles during sleep and runs one after it wakes if a cat used it.