GLAS
Fan Run‑On Not Controlled by Thermostat
Thermostat shows that the fan is off, but the indoor blower continues to run.
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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
Furnace fan delay setting, Stuck fan relay on furnace control board, G wire shorted to R, GLAS fan relay stuck closed
How to Fix / Troubleshooting
Safety warning: Turn off power to the furnace/air‑handler at the breaker before opening panels.
- Step 1 – Allow fan off‑delay: Many furnaces run the fan for several minutes after a heat call ends. Wait 5–10 minutes to see if it stops.
- Step 2 – Check GLAS fan mode: Ensure fan mode is set to Auto, not On or Circulate.
- Step 3 – Inspect G wiring: Check for shorts between G and R at the wall plate and furnace board.
- Step 4 – Isolate GLAS: Disconnect the G wire from the GLAS wall plate and restore power. If the fan still runs, the furnace control board relay is likely stuck. If it stops, GLAS or wiring is at fault.
- Step 5 – Call technician or replace GLAS: Replace the furnace control board if its fan relay is stuck, or replace GLAS if its G relay is stuck closed.
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Repair Difficulty
Hard
4/5
Required Part
Furnace Control Board Fan Relay or GLAS Main Control Board (G Relay)
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