E13
Johnson Controls
Fan Output Relay or G Circuit Fault
E13 displayed and thermostat indicates fan control fault; fan may run continuously or not at all.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Stuck fan relay on thermostat PCB, Shorted G wire to R, Miswired fan terminal at air handler, Failed fan relay on air handler control board
How to Fix / Troubleshooting
Safety: Turn off power to the furnace/air handler and thermostat at the breaker before working on wiring.
- Step 1 – Inspect thermostat wiring: Remove the thermostat and check the G terminal. Ensure the wire is secure and not touching R or other terminals.
- Step 2 – Inspect at air handler: At the control board, verify that the G wire is correctly landed and that there are no visible shorts or burned traces.
- Step 3 – Voltage test: Restore power. If the fan runs constantly, measure between R and G at the thermostat with no fan call. If 24 VAC is present, the thermostat is energizing G when it should not, indicating a stuck relay.
- Step 4 – Bypass test: With power off, temporarily remove the G wire from the thermostat. Restore power. If the fan stops running continuously, the thermostat is at fault.
- Step 5 – Replace faulty component: Replace the thermostat main control board if its fan relay is stuck, or have a technician replace the air handler fan relay/control board if the thermostat is not energizing G but the fan still runs.
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Repair Difficulty
Hard
4/5
Required Part
Main Control Board (Fan Relay) or Air Handler Control Board
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