H001
GLAS
Humidifier Control Output Fault
Thermostat displays H001 and will not activate the humidifier when humidity is low.
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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
Humidifier accessory not wired to GLAS HUM terminal, Loose HUM wire at wall plate or humidifier, Incorrect humidifier type configuration in GLAS, Failed HUM relay on GLAS main board
How to Fix / Troubleshooting
Safety warning: Turn off power to the furnace/air‑handler and humidifier at the breakers before working on wiring.
- Step 1 – Verify accessory wiring: Confirm the humidifier control wires are connected to the correct HUM or accessory terminals on the GLAS wall plate and to the humidifier or furnace board as per the GLAS manual.
- Step 2 – Check configuration: In GLAS settings, ensure the humidifier is enabled and the correct type (bypass, fan‑powered, steam) is selected.
- Step 3 – Continuity test: With power off, test continuity of the HUM control wires between GLAS and the humidifier or furnace board.
- Step 4 – Bypass test: With power on and caution, manually jumper the humidifier control terminals at the furnace board to see if the humidifier activates. If it does, the accessory is functional.
- Step 5 – Suspect GLAS HUM relay: If the humidifier works with a manual jumper but not when GLAS calls for humidity, the HUM relay on the GLAS main board may be failed. Replace the thermostat.
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Repair Difficulty
Hard
4/5
Required Part
GLAS Main Control Board (Humidifier Relay)
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