Nest
Open Heat Call Circuit or Furnace Lockout
Nest thermostat calls for heat but furnace does not start
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 W1 wire at Nest or furnace control board, Blown low‑voltage fuse on control board, Furnace in safety lockout due to previous fault, Faulty furnace control board heat relay
How to Fix / Troubleshooting
Safety: Turn off power to the furnace before opening panels.
- Check Nest status: Confirm the Nest shows that it is calling for heat (orange ring) and that the room temperature is below the setpoint.
- Inspect W1 wiring: Ensure the W1 wire is secure at the Nest base and at the furnace control board W/W1 terminal.
- Fuse check: Inspect the low‑voltage fuse on the control board and replace if blown.
- Furnace lockout: Turn off furnace power for 5 minutes, then restore power to clear a possible lockout. Observe any diagnostic LEDs on the control board for error codes.
- Direct jumper test: With the Nest removed and power on, briefly jumper R to W at the furnace control board. If the furnace starts, the issue is likely with the Nest or thermostat wiring. If it does not, the furnace control board or safety switches may be at fault and require professional service.
Advertisements
Repair Difficulty
Hard
4/5
Required Part
Furnace Control Board or W1 Heat Call Wire
Check Price on Amazon
We may earn a commission from links on this page.
Advertisements