G001
GLAS
Open G (Fan) Circuit
Thermostat shows G001 and the indoor blower fan does not run when heating or cooling is active.
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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
Loose or broken G wire at GLAS wall plate, Disconnected G terminal at furnace/air‑handler control board, Open thermostat cable conductor for G, Failed G relay output on GLAS main board
How to Fix / Troubleshooting
Safety warning: Turn off power to the furnace/air‑handler at the breaker before opening the unit.
- Step 1 – Inspect GLAS G terminal: Remove the thermostat and verify the G wire is fully inserted and clamped.
- Step 2 – Inspect furnace control board: With power off, confirm the G wire is connected to the G terminal and secure.
- Step 3 – Continuity test: Disconnect G at both ends and test continuity with a multimeter. Replace cable if open.
- Step 4 – Bypass test: With power on and caution, jumper R to G at the furnace control board. If the blower starts, the fan relay and motor are functional.
- Step 5 – Suspect GLAS relay: If the blower runs with an R‑G jumper but not when GLAS calls for fan, the G relay on the GLAS main board is likely failed. Replace the thermostat.
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Repair Difficulty
Hard
4/5
Required Part
GLAS Main Control Board (G Fan Relay)
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