Thermostat displays E7 and fan will not respond to commands or runs continuously

Safety first: Turn off power to the furnace/air handler at the breaker before accessing wiring.

• Step 1 – Check thermostat settings: Ensure the fan mode is not set to "On" or a continuous circulation mode that could be misinterpreted as a fault.
• Step 2 – Inspect G wiring: Remove the thermostat and inspect the G (fan) wire for frayed insulation or contact with other terminals. Tighten the terminal screw.
• Step 3 – Isolate thermostat: At the indoor unit, disconnect the G wire coming from the thermostat. Restore power. If the fan still runs continuously, the issue is in the indoor unit control board or a stuck fan relay.
• Step 4 – Test fan relay: With power off, inspect the indoor unit control board for signs of overheating or burnt traces near the fan relay. Replacement of the board is usually required if the relay is stuck.
• Step 5 – Replace thermostat/interface: If the fan does not run with G disconnected at the indoor unit but E7 persists, the thermostat or iComfort equipment interface module may have a failed output stage and should be replaced.