Thermostat shows F1 and indicates a fan control fault; indoor blower may not run or may run continuously.

Safety first: Turn off power to the furnace/air handler before working on wiring or control boards.

• Check G wiring: At the thermostat, verify the green G wire is firmly connected. At the indoor control board, confirm the same conductor is on the G terminal and is not loose or shorted to other wires.
• Test fan in ON mode: Restore power and set the thermostat fan to ON. If F1 appears and the blower does not run, the issue is likely in the wiring or indoor fan relay.
• Bypass thermostat (advanced): With power off, temporarily jumper R to G at the indoor control board. Restore power; if the blower runs normally, the thermostat or G wire is at fault. If it does not, the Payne control board or blower motor circuit is faulty.
• Inspect control board: Look for burned traces or relays on the Payne furnace/air handler control board. Replace the board if damage is visible and confirmed by testing.
• Replace thermostat if needed: If the blower runs with an R‑G jumper but F1 persists and the fan will not respond to thermostat commands, replace the thermostat.