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Fix a robot lawn mower that will not cut

We'll confirm the mower moves but does not cut, check battery and mode, inspect the blade and undercarriage, and rule out blade motor failure—or tell you when to call a pro.

Troubleshooting · Home appliances
15–30 min
What you'll need
  • Screwdriver or blade key (per your model)
  • Replacement blade (if inspection shows damage)
  • Stiff brush or scraper for undercarriage
Diagnostic graph validation issues: Terminal node n_blade_spins must have null branches
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Steps

Goal: Confirm the symptom, rule out battery and mode, then isolate the cutting fault.

  • Start a mowing cycle and watch the mower.
  • Good: The mower moves but the grass stays uncut—cutting system has failed. Proceed to Check battery and mode.
  • Bad: The mower does not move at all—different problem (battery, boundary wire, drive motor). See When to get help.

Check battery and mode

Goal: Rule out low charge and wrong mode before inspecting the blade.

  • Confirm the battery is charged. Check the app or display for charge level. A low battery can cause the mower to return early or skip cutting.
  • Confirm the charging station is plugged in and the contacts are clean.
  • Check that the mower is in mowing mode with a valid schedule. Some mowers patrol without cutting if not in mowing mode.
  • Check the cutting height. If set too high, the blade may not reach the grass. Lower one notch and test.
  • Good: Battery full, mode correct, height reasonable. Proceed to Blade and undercarriage path.
  • Bad: Low battery or wrong mode—fix those first.

Blade and undercarriage path

Goal: Inspect and fix the blade and undercarriage so the blade can cut.

  • Turn off the mower and remove the battery. Tip the mower to access the blade.
  • Inspect the blade for dullness, bends, chips, or cracks. Confirm it is installed correctly per your manual. Tighten the blade bolt if loose. Replace the blade if damaged.
  • Clean the undercarriage. Scrape or brush away grass and debris. Remove any wrapped grass from the blade spindle.
  • Reinstall the battery and run a mowing cycle. Listen for the blade motor. You should hear it and see grass being cut.
  • Good: Blade is sharp and attached, undercarriage is clear, blade spins—mower should cut.
  • Bad: Blade does not spin when the mower runs—blade motor has likely failed. Call a technician.

When to get help

Call a technician or authorized service if:

  • The mower does not move at all (different problem—see drive or charging guides).
  • The blade motor does not spin when the mower runs.
  • You hear grinding or unusual noise from the blade area.
  • You have replaced the blade and cleaned the undercarriage and it still does not cut.

Do not open the motor housing or attempt blade motor repair yourself.

Verification

  • The mower moves across the lawn and the blade spins.
  • Grass is cut to the expected height.
  • No grinding or unusual noise from the blade area.
  • The blade is sharp, firmly attached, and the undercarriage is clear of buildup.

Escalation ladder

Work from the device outward. Stop when the problem is fixed.

  1. Confirm symptom Verify the mower moves but the grass stays uncut; rule out drive or boundary issues.
  2. Battery and mode Check charge level, mowing mode, and schedule.
  3. Cutting height and blade Adjust cutting height; inspect and replace blade if dull or damaged.
  4. Clean undercarriage Remove grass buildup under the deck that blocks the blade.
  5. Call a pro Blade motor does not spin, grinding noise, or repeated failures—call a technician.

What to capture if you need help

Before calling support or posting for help, have these ready. It speeds everything up.

  • Mower brand and model
  • Whether the mower moves and the blade spins
  • Cutting height setting
  • Blade condition (dull, bent, loose)
  • Steps already tried

Does the mower move but the grass stay uncut?

Start a mowing cycle and watch. If the mower drives across the lawn but the grass remains standing, the cutting system has failed. If the mower does not move at all, that is a different problem.

Start a mowing cycle and watch the mower. Good: mower moves but grass stays uncut—cutting fault. Bad: mower does not move—different problem (battery, boundary wire, drive motor); see drive or charging guides.

Yes No

You can change your answer later.

Is the battery charged and the mower in mowing mode?

Low battery or wrong mode can prevent cutting. Check the app or display.

Confirm the battery is charged and the mower is in mowing mode with a valid schedule. Check cutting height—if set too high, the blade may not reach the grass. Good: battery full, mode correct, height reasonable. Bad: low battery or wrong mode—charge the battery and set mowing mode, then retest.

Yes No

You can change your answer later.

Fix battery and mode, then retest

Charge the battery fully. Set the mower to mowing mode and confirm a valid schedule. Adjust cutting height if too high. Run a mowing cycle. If it still does not cut, proceed to inspect the blade and undercarriage.

Done

Is the blade sharp, straight, and correctly installed?

A dull, bent, or loose blade will not cut. Check the blade and its orientation.

Turn off the mower and remove the battery. Tip the mower to access the blade. Check for dullness, bends, chips, or cracks. Confirm correct installation per your manual. Tighten if loose. Replace if damaged. Good: blade is sharp, straight, and firmly attached. Bad: blade damaged or wrong—replace and test.

Yes No

You can change your answer later.

Replace blade and test

Replace the blade with a matching part. Reinstall per your manual. Test a mowing cycle. The mower should cut. If it still does not cut, proceed to clean the undercarriage.

Done

Is the undercarriage clear of grass buildup?

Grass and debris under the deck can block the blade from spinning.

Turn off the mower and remove the battery. Tip the mower and scrape or brush the undercarriage clean. Remove any wrapped grass from the blade spindle. Good: undercarriage clear. Bad: buildup present—clean and test.

Yes No

You can change your answer later.

Clean undercarriage and test

Clean the undercarriage and blade spindle. Reinstall the battery and run a mowing cycle. The mower should cut. If it still does not cut, check whether the blade spins when the mower runs.

Done

Does the blade spin when the mower runs?

If the mower moves but the blade does not spin, the blade motor has likely failed.

Start a mowing cycle and listen. You should hear the blade motor and see grass being cut. Blade spins: cutting should work—recheck height and blade sharpness. Blade does not spin: blade motor has likely failed—call a technician. Do not open the motor housing yourself.
Question

Does the blade spin when the mower runs?

Done

Call a technician

Call a technician or authorized service if: the mower does not move at all (different problem); the blade motor does not spin when the mower runs; you hear grinding or unusual noise from the blade area; or you have replaced the blade and cleaned the undercarriage and it still does not cut. Do not open the motor housing or attempt blade motor repair yourself.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

Why would a robot lawn mower move but not cut?
Common causes: cutting height set too high, dull or damaged blade, loose or incorrectly installed blade, grass buildup under the deck blocking the blade, or a failed blade motor. Check mode and schedule first—some mowers will patrol without cutting if not in mowing mode.
Can I fix a robot lawn mower that will not cut myself?
Yes. You can adjust cutting height, sharpen or replace the blade, clean the undercarriage, and confirm the mower is in mowing mode. Blade motor replacement usually requires a technician or authorized service.
When should I call a technician for a robot lawn mower?
Call a technician if the blade motor does not spin when the mower runs, you hear grinding or unusual noise from the blade area, or you have tried blade replacement and cleaning and it still does not cut. Do not open the motor housing yourself.

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