Display shows F15; opener operates but external accessories (loops, key switches) malfunction.

Safety first: Turn off power before changing accessory wiring.

• 1. Identify accessories: Note all devices connected to the Linear opener’s accessory terminals (key switch, loop detector, timer, etc.).
• 2. Disconnect accessories: Remove all accessory wires from the control board. Restore power and see if F15 clears.
• 3. Reconnect one at a time: With power off, reconnect each accessory individually, powering up and testing after each. The device that causes F15 to return is likely faulty or miswired.
• 4. Check wiring diagrams: Verify each accessory is wired to the correct terminals and that any required dry contacts or power supplies are used as specified by Linear.
• 5. Replace faulty accessory or repair wiring: Correct any shorts or miswiring. Replace defective external devices.
• 6. Replace control board if needed: If F15 persists with all accessories removed, the accessory input circuitry on the board may be damaged and the board should be replaced.