Litter-Robot 4 not cycling: find the cause from the light bar
Different model? Litter-Robot 5 owners: see Litter-Robot 5 not cycling. Litter-Robot 3 owners: start with the Litter-Robot 3 troubleshooting guide.
- Read the light bar first — its color tells you which of the causes below is blocking the cycle.
- Rule out the settings — the default cycle delay is 7 minutes, and a purple light means Sleep Mode (8 hours) is on. Neither is a fault.
- Reset the weight scale — remove litter above the fill line, make sure all four feet sit on a hard floor, then press Reset twice from the Home position.
- Clean the sensors — wipe the bezel with a dry cloth and vacuum the inside edge of the globe opening.
- Your cat used it, nothing happened — the globe stays in place long after your cat has left, and waste sits in the litter bed.
- The Cycle button still works — a manual cycle runs normally, but automatic cycles never start on their own.
- The light bar is not plain blue — it is purple, red, flashing blue, blue with flashing yellow, or alternating two colors, or the Whisker app shows an "Extended scale activity" notification.
Your cat can still use the box, but cycles aren’t reliable. Scoop once by hand today so waste doesn’t sit in the globe overnight.
Why a Litter-Robot 4 stops cycling on its own
The Litter-Robot 4 only starts an automatic cycle when three things line up: its sensors saw a cat come in and leave, the countdown after the visit has finished, and nothing on the unit says "unsafe to rotate". When any of the three is missing, the globe waits, and the light bar shows what it is waiting for.
A setting is holding the cycle back
After your cat leaves, the unit waits for the cycle delay (7 minutes out of the box, up to 30) before rotating, and restarts the countdown if the cat comes back. Sleep Mode goes further: for 8 hours every day the unit watches for a cat but does not clean. Both look like a breakdown, and neither is one.
The weight scale lost its zero
Weight sensors in the base confirm that a cat is inside. Too much litter, a mat or cord under one foot, a soft or uneven floor, or a freshly emptied drawer can shift the baseline so the unit thinks something is still in the globe. After 30 minutes it stops and signals excess weight.
Dusty sensors or a full drawer
Curtain sensors in the bezel watch the globe opening. Litter dust or fur on them reads as a cat that never leaves. Separately, when the drawer full indicator decides the drawer is full, automatic cycling pauses until you empty it.
A light cat or a motor problem
Whisker specifies a minimum of 3 lb for automatic mode: a kitten below that may never register. Less often, the motor connection or the globe itself is the problem, and the light bar shows a fault pattern instead of plain blue.
Start by matching your light bar to the table below, then follow the steps. Most units are cycling again within 15 minutes.
| Light bar | What it means | Go to |
|---|---|---|
| Solid red | Cat detected, cycle delay counting down | Step 1 |
| Solid purple | Sleep Mode period in progress | Step 2 |
| Flashing blue | Waste drawer full (or the DFI thinks so) | Step 3 |
| Blue + partial yellow flashing (red flashing on firmware 2.86 and older) |
Scale triggered for 30+ minutes, "Extended scale activity" | Steps 4–5 |
| Red and blue alternating | Curtain sensors need cleaning | Step 6 |
| Blue and white alternating | Motor connection problem | Step 7 |
| Solid blue, still no cycle | Cat not detected (weight, placement) | Step 5 and 04 |
How to fix it, light by light
Work through the steps in order: the first ones cost nothing and cover the most common cases. Tick each step as you go.
Litter-Robot 4 on carpet?
Soft flooring is one of the most common reasons the scale drifts and the unit stops cycling. The official Carpet Tray gives the feet a rigid base.
If the issue persists: replacement options
If the light bar stays plain blue, manual cycles work, the scale has been zeroed on a hard floor, and your cat still never triggers an automatic cycle, the weight sensors in the base are the most likely cause. Whisker's own guidance for a scale fault that survives these steps and a firmware update is to replace the base. Contact Whisker first if your unit is still under warranty: WhiskerCare covers replacement parts.
Out of warranty on an older unit with several failing parts? A complete Litter-Robot 4 bundle may cost less than a base plus repeated repairs.
As an Amazon Associate, Pet Infrastructure earns from qualifying purchases. We may receive a commission when you buy through our links, at no extra cost to you. Links to whisker.com and litter-robot.com earn us nothing.
Before ordering anything, check the less common cases below.
Less common cases
These situations are rarer, but they explain most of the units that still refuse to cycle after Part A and Part B.
My cat is a kitten or very small
Whisker does not recommend automatic mode for cats under 3 lb: their weight and size may not activate the cat sensing system, so the unit never knows a visit happened. That is a safety limit, not a fault. Until your kitten passes 3 lb, the manual recommends a semi-automatic routine: leave the unit off, and after your kitten has used it, turn it on, press Cycle, and turn it off again once the cycle is done (about 2 minutes).
It stopped cycling right after I added the LitterHopper
The LitterHopper adds its own weight and its own light patterns (blue and purple alternating, or a "scale active" pattern). If the problem began the day you installed it, go to our Litter-Robot 4 LitterHopper setup and fix guide before anything else.
Manual cycles work, automatic never has
If a brand-new unit has never cycled automatically, even after a factory reset, lowered litter and several cats, the cat sensing hardware is the suspect. One owner documented exactly this case on the RobotShop community forum in early 2023: manual cycles worked, the red light stayed on after every visit, and Whisker ended up exchanging the unit. On a new unit, contact Whisker rather than buying parts.
Before you call, make sure the firmware is current (the Whisker app offers the update when one exists) and note which light pattern you see: support will ask for both.
The globe starts, then stops partway
That is a different problem: the cycle starts but is interrupted. A yellow "ping-pong" light bar means the anti-pinch safety stopped it, and a flashing yellow light means the bonnet is not seated: see our Litter-Robot 4 pinch detect and bonnet error fix. For every other light code, the Litter-Robot 4 troubleshooting guide lists them all in one place.
Frequently asked questions
Why is my Litter-Robot 4 not cycling after my cat uses it?
Look at the light bar. Solid red means the cycle delay (7 minutes by default) is still counting down, purple means Sleep Mode, flashing blue means a full drawer, and blue with partial yellow flashing means the weight scale needs to be reset. Each has a quick fix in the steps above.
How do I force my Litter-Robot 4 to cycle?
Press the Cycle button with the globe at the Home position to start a clean cycle right away. If the light bar is solid red, pressing Reset cancels the countdown instead, and the unit returns to Ready Mode on a blue light.
How do I reset the weight sensor on a Litter-Robot 4?
Make sure nothing is touching the unit and the litter is at or below the MAX fill line, then press the Reset button twice from the Home position. That zeroes the scale. Run a test cycle with the Cycle button: it should end on a solid blue light.
Why does my Litter-Robot 4 say "Extended scale activity"?
That app notification means the weight scale has been triggered for more than 30 minutes, usually because of too much litter, a mat or cord under a foot, or a soft floor. The unit shows blue with partial yellow flashing. Remove the excess, fix the placement, and press Reset twice from the Home position.
Conclusion
A Litter-Robot 4 that won't cycle is usually waiting for something, not broken: a countdown, a sleep period, a full drawer, or a scale that needs re-zeroing. Read the light bar, work through the steps, and in most homes the next visit ends with a clean cycle. If yours still refuses, note the exact light pattern and your firmware version before contacting Whisker: it shortens the call.
Still not fixed? Here’s what to do next.
Some faults are genuinely hardware, and no amount of cleaning or resetting will clear them. If you’ve worked through everything above and it’s still doing it, stop here rather than taking the unit further apart.
- Go to Whisker (Litter-Robot) directly. If the unit is still under warranty, let them replace the part rather than paying for it yourself — contact Whisker (Litter-Robot) support.
- Tell us what didn’t work. We rewrite bulletins when readers show us a case they don’t cover — compliance@pet-infrastructure.com. Tell us the model, what the lights are doing, and which steps you already tried.
- Ask other owners. r/litterrobot is active and full of people who have had the exact same fault on the exact same model. Search the sub before posting — the answer is often already there.
When to stop and call the manufacturer: if the fix needs the base opened, the motor or control board touched, or any tool beyond a screwdriver — stop. On a unit in this price range, opening it yourself usually voids the warranty, and a warranty repair costs nothing.
Did this actually fix it? 🐾
The complete Litter-Robot 4 bulletin library
Every Litter-Robot 4 bulletin published on the site, in one place:
| Bulletin | Covers |
|---|---|
| TB-LR4-001 | Solid red, flashing red, red with yellow, red with blue: here is what each… |
| TB-LR4-002 | Litter-Robot 4 flashing blue with an empty drawer? Clean the OmniSense laser sensors… |
| TB-LR4-003 | Blue and white lights, or 'Overloaded Globe' in the app? It's usually litter packed in… |
| TB-LR4-004 | Litter-Robot 4 won't connect to Wi-Fi or keeps going offline? Fix blinking yellow… |
| TB-LR4-005 | Litter-Robot 4 app showing wrong status, stuck offline, or not updating? Clear… |
| TB-LR4-006 | Litter-Robot 4 malfunctioning, cycling stuck, or smelling despite regular cleaning?… |
| TB-LR4-007 | Liner not dropping, or waste sticking after each cycle? Usually the liner weight has… |
| TB-LR4-008 | Litter-Robot 4 LED panel keeping you up at night? Learn how to turn off the Night… |
| TB-LR4-009 | Official Litter-Robot 4 liners cost $12–$55 plus shipping. See the exact waste drawer… |
| TB-LR4-010 | Litter-Robot 4 showing only a blinking blue Power button after an outage? Learn what… |
| TB-LR4-011 | A sourced reliability report on the Litter-Robot 4 beyond warranty — documented… |
| TB-LR4-012 | Litter-Robot 4 stuck on a yellow ping-pong light, green-and-white flash, or bonnet… |
| TB-LR4-013 | Small flies around your Litter-Robot? Moist waste-drawer residue attracts phorid… |
| TB-LR4-014 | Litter-Robot 4 still smells within hours of a full teardown clean? Worn seal strips,… |
| TB-LR4-015 | Litter-Robot 4 dumping clean, unused litter into the waste drawer? Learn the three… |
| TB-LR4-016 | Litter-Robot 4 carbon filter needs replacing? Here's exactly where it sits, how to… |
| TB-LR4-017 | Litter-Robot 4 panel flashing blue and purple, or just unboxed the LitterHopper?… |
| TB-LR4-018 | The complete Litter-Robot 4 maintenance guide: daily cleaning routine, odor fixes,… |
| TB-LR4-019 | Litter-Robot 4 acting up? Match your exact light, connectivity, or odor issue to the… |
| TB-LR4-020 | Cleaning and resetting didn't clear the fault? Compare the Litter-Robot 4 motor… |
| TB-LR4-021 | Three Litter-Robot 4 laser boards sell for $50 under different SKUs. Which one matches… |
| TB-LR4-022 | A new Litter-Robot 4 motor that faults again within days points somewhere else. What… |
| TB-LR4-023 | A carbon filter only treats the air that passes through it. How to size and place a… |
| TB-LR4-025 | Position fault on your Litter-Robot? What it means on the LR3, LR4, LR5 and EVO, how… |
Written by Alberto Guardia
I’m a physician working in medical informatics, and I run Pet Infrastructure on my own — no team, no manufacturer sponsorship, no paid placements. I share my home with Wolfgang, a 13-year-old Chartreux with firm opinions about litter and none whatsoever about firmware.
How this page was put together. Every light code, button sequence and timing here is traced back to Whisker (Litter-Robot)’s own documentation, to official support articles, or to several owner reports that agree with each other — and the guide tells you which. Where something genuinely isn’t documented anywhere, I say so instead of filling the gap.
How I check every guide → · Last updated September 2026