Litter-Robot Troubleshooting: Not Sensing Cat, Yellow Light, Not Cycling & Drawer Full (LR3, LR4 & LR5)

Your cat uses the box and nothing happens. Or the globe stopped mid-cycle. Or it’s flashing yellow. Or it insists the drawer is full when it isn’t. Here are the most common Litter-Robot 3, 4, and 5 problems — and exactly how to fix each one.

Last updated: August 14, 2026 • How we review →

Quick Diagnostic Table

Litter-Robot Not Sensing Cat: Weight Detection Fixes for LR3 and LR4

Symptom: Your cat goes in, does their business, and leaves — and the unit never starts a cycle. No countdown, no rotation, and on a connected model no visit logged in the app.

Why it happens: Both models detect a cat by sensing added weight, so anything that interferes with a clean weight reading looks identical to “no cat was here.” The mechanism differs between the LR3 and LR4, so work through the section for the model you actually own.

Litter-Robot 3 not sensing cat

1. Confirm the unit is level and nothing is touching the globe. A wall, a baseboard, a litter mat wedged under one foot, or a power cord trapped beneath the base all absorb the weight change the sensor is looking for. The unit must stand free on a flat, hard, level surface.
2. Check for litter overfill. Litter above the fill line adds constant baseline weight and eats into the sensor’s usable range. This is the single most common cause.
3. Run a clean calibration. Power off, lift the globe off, wipe the seating ring and the base rim free of litter granules, reseat the globe flush, power back on, and let one full cycle complete with no cat present.
4. Check the published minimum cat weight for your model. Whisker specifies a minimum weight in the LR3 manual — kittens and very small cats below that threshold will not reliably trigger detection, and that is expected behaviour rather than a fault. Confirm the exact figure in your manual before troubleshooting further.
5. Inspect the base contact points. Spilled litter or dried waste under the globe’s seating ring shifts the reading permanently. Vacuum it out.

If the unit still registers nothing after a clean calibration on a level floor with litter at the correct level, the load sensor itself is the likely failure — that is a Whisker warranty item, not a user repair.

Litter-Robot 4 not detecting cat

1. Reseat the globe into the bezel. The LR4 will not read weight correctly unless the globe is fully clicked in. This is the fix that resolves most sudden-onset LR4 detection failures.
2. Level the unit. The LR4’s weight sensing is noticeably less tolerant of tilt than the LR3’s. A slightly uneven floor is enough to skew readings.
3. Clear litter dust from the base. Granules and compacted dust under the globe interfere with the weight plate.
4. Check whether visits are being logged to the wrong cat. If the app shows visits but attributes them incorrectly, that is a cat-identification problem, not a detection failure — the LR4 separates cats by weight, so similarly sized cats get merged or swapped.
5. Recalibrate from the Whisker app, then run one empty cycle before concluding the hardware has failed.

Still nothing after calibration? Work through the LR4-specific walkthrough: Litter-Robot 4 problems and fixes →

Problem 1: Flashing Yellow Light

What it means: The cycle was interrupted — either the cat re-entered, the safety sensor triggered, or the unit detected an obstruction.

1. Press the Reset button (or Cycle button on LR3) to clear the warning
2. Check that nothing is stuck in or around the globe
3. If it triggers repeatedly, the litter level may be too high — fill only to the fill line
4. If your cat re-enters mid-cycle frequently, increase the cycle delay in the Whisker app to 7-15 minutes

Yellow plus another colour at the same time? Light-colour combinations — blue and yellow together, for example — are model-specific codes, and the LR3 and LR4 do not use the same chart. Note the exact pattern first: which lights are lit, and whether each is solid or flashing. Then check the light-code chart in your model’s manual. Resetting the unit clears the code, so record it before you reset if you may need to describe it to Whisker support.

Problem 2: Flashing Red Light / Cat Sensor Fault (LR3 and LR4)

What it means: The cat sensor detected a fault — typically the unit thinks something is wrong with the weight reading.

1. Power off the unit (unplug from wall)
2. Remove the globe completely
3. Check that the unit is on a level surface — even slight tilt affects weight sensors
4. Inspect the weight sensor area at the base for debris or litter contamination
5. Reseat the globe firmly. Power back on. Run an empty cycle to recalibrate.

If red flashing persists, contact Whisker support. For LR4-specific sensor issues, see our LR4 problems guide. If the unit is not faulting but simply never registers your cat, that is a different problem — see not sensing cat above.

Problem 3: Litter-Robot Not Cycling / Globe Stuck Mid-Rotation

What it means: The globe will not complete a cycle, or stopped partway through one. Usually caused by litter overfill or a clump wedged into the sift mechanism.

1. Power off and unplug
2. Manually rotate the globe back to home position (slowly, both hands)
3. Empty the globe completely. Check the rotation mechanism at the base for stuck litter clumps.
4. Vacuum out any loose litter from inside the base unit
5. Refill litter to the fill line — not above

If the globe never starts a cycle at all — rather than starting and stopping — the unit is probably not registering the cat in the first place. Check not sensing cat before dismantling anything.

Most common cause of a stalled cycle: wrong litter. Stick with medium-grain clumping clay. See our guide to litter for automatic boxes and our litter guide for Litter-Robot specifically.

Get Dr. Elsey’s Ultra (Prevents Jams) →

Problem 4: Cycles Constantly Without a Cat Using It

What it means: The infrared sensor is being falsely triggered. Almost always caused by dust accumulation on the sensor.

1. Locate the cat sensor port (small opening inside the globe entrance)
2. Use a dry microfiber cloth to wipe the sensor lens — do not use water or solvents
3. Compressed air can clear deeper dust accumulation
4. Switch to a lower-dust litter (Dr. Elsey’s Ultra has the lowest dust profile of major brands)

Switch to Dr. Elsey’s (Lowest Dust) →

Problem 5: Won’t Connect to WiFi

1. The Litter-Robot only supports 2.4GHz WiFi networks. Enable 2.4GHz on your router if needed.
2. If your network uses one SSID for both bands, temporarily separate them during setup.
3. Hold the Reset button for 8 seconds to factory reset the WiFi module
4. Re-pair through the Whisker app from scratch

Problem 6: Cat Refuses to Use the Litter-Robot

This is behavioral, not mechanical.

1. Don’t force adoption. Keep the old box right next to the new one for 2-3 weeks minimum.
2. Turn off auto-cycling initially. Let your cat investigate at their own pace.
3. Use familiar litter. Don’t change litter brands at the same time.
4. If the cat absolutely refuses after 4+ weeks: Some cats reject enclosed globe designs. See our alternatives guide.

Problem 7: Strong Odor Inside the Globe

1. Empty the waste drawer (every 2-7 days depending on cat count)
2. Replace the carbon filter — they typically last 2-3 months
3. Do a full deep clean monthly: empty all litter, wipe the globe interior with white vinegar solution, rinse, dry before refilling
4. Use a quality clumping litter — cheaper litters break apart and leave residue

No verified exact-match carbon filter listing yet — search “Litter-Robot 4 carbon filter” on Amazon to find current replacement filters.

Litter-Robot Says “Drawer Full” When It Isn’t

What it means: The drawer indicator is triggered by weight, not by looking at how full the drawer is. A false “drawer full” almost always means the unit is weighing something that isn’t waste.

1. Reseat the drawer. Pull it fully out and push it back until it seats firmly. A partially seated drawer reads as loaded.
2. Clean the contact area between drawer and base. Compacted litter dust on the contact points inflates the reading.
3. Check the liner. A liner bunched underneath, or a heavy-duty bag doubled over, can add enough weight to trip the threshold on its own.
4. Look for waste stuck to the drawer walls after a jam. It stays on the scale even after the drawer looks empty.
5. Level the unit. Same root cause as sensor faults — a tilted unit distributes weight unevenly.
6. Empty, wipe dry, reseat, then let one full cycle complete before judging whether the warning cleared.

If the warning returns immediately on a clean, empty, correctly seated drawer standing on a level floor, the drawer sensor is the likely fault — contact Whisker support.

Litter-Robot 3 Troubleshooting: What’s Different from the LR4

Most troubleshooting advice online is written for the LR4 and quietly assumes you own one. If you have an LR3 or LR3 Connect, several steps above change:

On a non-Connect LR3 you have no app diagnostics at all — the light pattern is the entire signal. Photograph the pattern before you power-cycle the unit, because a reset clears exactly the information Whisker support will ask you to describe.

Everything in not sensing cat, not cycling, drawer full, and odor applies to the LR3 as well — substitute the Cycle button wherever this guide says Reset.

Is It Time to Upgrade to the Litter-Robot 5?

If your LR4 has failed repeatedly outside warranty — or you’re managing 3+ cats — consider the LR5. Real upgrades: per-cat AI health tracking, quieter QuietSift motor, multi-cat ID.

Preventive Maintenance Checklist

Frequently Asked Questions

Why is my Litter-Robot not sensing my cat?

Almost always a weight-reading problem rather than a broken sensor: the unit isn’t level, something is touching the globe, litter is filled above the line, or the globe needs reseating and recalibration. Full step-by-step for both models: Litter-Robot not sensing cat →

Why does my Litter-Robot keep saying “drawer full” when it’s not?

The drawer sensor reads weight, not visual fullness — so the fix is usually reseating and cleaning rather than emptying. Full walkthrough: drawer full when it isn’t →

Why won’t my Litter-Robot cycle?

If it starts and stops partway, treat it as a jam or overfill — see not cycling / globe stuck. If it never starts at all, the unit likely never registered the cat — see not sensing cat.

How long should a Litter-Robot last?

The LR3 and LR4 are designed for 7-10 years with proper maintenance. Most failures happen at 3-5 years — weight sensor or motor issues Whisker typically resolves under warranty.

Can I use the Litter-Robot without WiFi?

Yes. WiFi adds app features but the unit operates fully without it using just the physical controls. On a non-Connect LR3 this is the only mode available, which is why light codes matter more on that model.

LR4 vs LR5 — which problems differ?

Most fixes here apply to both. LR4-specific issues: LR4 problems guide. Upgrade comparison: LR4 vs LR5.

Related Reading

— From our cats to yours 🐾

Related guides: Best Litter-Robot Alternatives (6 compared) · Best Litter for the Litter-Robot

Prefer everything in one order? The Litter-Robot 4 Supply & Accessory Bundle (US) packages the LR4 with the filters, liners, and accessories most owners end up buying anyway — if you’ll use the supplies, it can work out to better value than piecing them together separately. Note it is a bundle, not the standalone unit, so compare the total against the plain LR4 before choosing.