Robot mower will not start mowing; display shows E1 shortly after pressing START.

Safety first: Turn the main power switch OFF and remove the battery or key (if equipped) before working on the mower. Wear cut‑resistant gloves; blades can be sharp even when not moving.

Step-by-step checks:

• 1. Place mower on level ground: Ensure the Yard Force robot is on flat, firm ground with all wheels touching. Turn the main switch ON and try to start again. E1 can appear if the mower is on a slope or one wheel is hanging.
• 2. Inspect lift sensor area: On most Yard Force models, the lift sensor is integrated into the chassis near the front or center. Check underneath for packed grass, mud, or stones that may hold the shell slightly open or press on the sensor. Clean with a brush and low‑pressure air.
• 3. Check chassis fit: Make sure the upper cover is fully seated and latched. A misaligned cover can keep the lift sensor in a triggered position.
• 4. Inspect wiring: With power OFF, remove the top cover (usually a few Torx screws). Locate the lift sensor connector on the main PCB. Ensure the plug is fully seated and wires are not pinched or broken.
• 5. Basic sensor test: With the mower supported safely and blades disabled, gently lift the front of the mower and watch the display. The error should appear only when lifted and clear when set down. If E1 remains even when flat, the sensor or PCB may be faulty.
• 6. Replace lift sensor if needed: If the sensor is visibly damaged or the wiring is intact but the error persists, replace the lift sensor assembly specific to your Yard Force model. Reassemble and retest.

When to call a technician: If you suspect a main PCB fault or are not comfortable opening the housing, contact an authorized Yard Force service center.