The furnace does not respond to the thermostat; the LED status light is on solid with no flashes.

Safety: Turn off the power before touching low-voltage wiring.

Steps to check:

• Verify thermostat settings: Set the thermostat to HEAT and raise the setpoint above room temperature. Confirm that batteries (if used) are good.
• Check thermostat wiring: At the furnace control board, verify that the R and W wires are securely connected. With the power off, inspect for breaks or loose connections along the cable.
• Bypass the thermostat (test only): With the power off, temporarily connect a jumper between R and W at the control board. Restore power. If the furnace starts, the thermostat or its wiring is likely faulty. Remove the jumper after testing.

When to call a technician: If the furnace does not respond even when R and W are jumpered, the control board or safety circuits may be at fault and require professional diagnosis.