App or thermostat shows 'Heat Not Responding' and home does not warm up

Safety: Turn off power to the furnace/air handler at the breaker before touching wiring.

• Verify thermostat mode and setpoint: Ensure the thermostat is in Heat mode and the set temperature is above room temperature.
• Inspect W terminal wiring: Remove the thermostat and confirm the W (or W1) wire is fully inserted and clamped. At the furnace control board, verify the same wire is secure at the W terminal.
• Check furnace fuse and status lights: Inspect the low‑voltage fuse on the control board and replace if blown. Observe any diagnostic LEDs and refer to the furnace manual.
• Confirm system configuration: In the thermostat installer setup, verify that the system type (conventional, heat pump, number of stages) matches your equipment.
• Bypass test (advanced): With power off, temporarily jumper R to W at the furnace board. Restore power; if the furnace starts, the issue is likely with the thermostat or thermostat wiring. If it does not, the furnace or control board needs service.