Robot lawnmower will not start mowing; display shows E01 immediately after power‑on.

Safety first: Place the mower on a flat surface, switch the main power OFF, and remove the battery or pull the main fuse if accessible before opening any covers.

• Check the red STOP button: Ensure the large red stop button on the NAC robot mower top cover is fully released. Press it down firmly and then twist or pull (depending on model) to reset.
• Clean around the button: Dirt and grass can jam the button. Use a soft brush and compressed air to clean the button perimeter. Do not use high‑pressure water.
• Inspect button travel: With power OFF, press the button repeatedly. It should move freely and spring back. If it feels sticky or does not return, the stop button switch assembly may be faulty.
• Check wiring (for experienced users): Remove the top cover according to the NAC service manual. Locate the stop button wiring harness going to the main control board. Look for loose connectors, corrosion, or damaged insulation. Reseat the connector firmly.
• Power cycle: Reinstall covers, reconnect battery, and turn the main switch ON. Clear the E01 code by pressing START. If the error persists after cleaning and reseating connectors, the stop button assembly or main PCB likely needs replacement.

Warning: Do not bypass or short the stop button; this is a critical safety device. If you are unsure, contact a qualified NAC service technician.