Door reverses randomly during travel; display shows F9; no obvious obstruction.

Safety first: Ensure the area under the door is clear during testing. Do not stand under a moving door.

• 1. Inspect full travel path: Slowly move the door manually through its full range and feel for any tight spots. Correct track alignment, roller issues, or hinge binding.
• 2. Re-learn travel limits: Follow the Linear manual to erase and reprogram the open and close limits. Many models require holding the Learn button and running a full open/close cycle.
• 3. Recalibrate force (if supported): Some Linear openers auto-calibrate force during the learn cycle. Ensure the door moves smoothly so the calibration is accurate.
• 4. Test with 2x4 obstruction: Place a 2x4 flat on the floor under the door and close. The door should reverse upon contact. If it reverses early or erratically, the force sensor circuit may be failing.
• 5. Replace control board: If mechanical issues are ruled out and recalibration does not resolve F9, replace the main control board which contains the force sensing electronics.