LiftMaster opener stops and reverses or will not move; UP arrow LED blinks once repeatedly.

Safety: Do not bypass safety sensors; they are required for safe operation.

• Check sensor LEDs: Each LiftMaster safety sensor has an LED. One is usually solid (sending), the other should be solid when aligned (receiving). If one or both are off or flickering, alignment or wiring is suspect.
• Realign sensors: Loosen the wing nuts on the sensor brackets. Aim the sensors directly at each other at the same height (about 4–6 inches above the floor). Tighten the nuts once both LEDs are solid.
• Remove obstructions: Clear any objects, cobwebs, or debris from the sensor path.
• Inspect wiring: Check the low-voltage wires from sensors to the opener for staples driven too tight, cuts, or corrosion at connections.
• Test operation: Once both sensor LEDs are solid, try closing the door from the wall button and remote.