Thermostat is on but will not turn on heating when temperature is set higher than room temperature

Safety first: Turn off power to the furnace/air handler before working on wiring.

• Step 1 – Verify mode and setpoint: Ensure the thermostat is in Heat or Auto mode and the setpoint is at least 2–3°F above the displayed room temperature.
• Step 2 – Check schedule/hold: Make sure an energy‑saving schedule is not overriding your manual setpoint. Use a temporary hold to test.
• Step 3 – Inspect W wiring: Remove the thermostat and verify that the W/W1 wire is securely connected and not broken.
• Step 4 – Test furnace response: At the furnace control board, temporarily jumper R to W. If the furnace starts, the issue is with the thermostat or its wiring. If it does not, the problem is in the furnace.
• Step 5 – Check configuration: In installer setup, confirm that the correct heat source (gas furnace, electric, heat pump) is selected and that heating stages are enabled.
• Step 6 – Replace thermostat/interface: If wiring and configuration are correct and the furnace responds to a manual jumper but not to the thermostat, the thermostat or equipment interface module heat output is likely defective and should be replaced.