GLAS
Heat Call Not Reaching Furnace
The thermostat calls for heat, but the furnace does not start; no error code is displayed on the GLAS.
Advertisements
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.
Advertisements
Possible Causes
Loose W wire, furnace safety lockout, blown furnace fuse, failed furnace control board relay
How to Fix / Troubleshooting
Safety warning: Turn off the power to the furnace at the breaker before opening any panels.
- Step 1 – Verify GLAS is calling for heat: Confirm that the thermostat shows a heating demand (heat icon or status).
- Step 2 – Inspect W wiring: Check the W wire at the GLAS wall plate and the furnace control board for secure connections.
- Step 3 – Check furnace status: Look for LED error codes on the furnace control board and follow the furnace manual for diagnostics.
- Step 4 – Bypass test: With the power on and using caution, jumper R to W at the furnace board. If the furnace starts, the issue is between the GLAS and the board. If it does not, the furnace itself needs service.
- Step 5 – Call HVAC technician: If the furnace does not respond to an R-W jumper, contact a professional to diagnose the furnace control board, pressure switches, or the ignition system.
Advertisements
Repair Difficulty
Professional Required
5/5
Required Part
Furnace Control Board or GLAS Main Control Board
Check Price on Amazon
We may earn a commission from links on this page.
Advertisements