Sensi thermostat screen is completely blank and unresponsive

Safety first: Turn off power to the furnace/air handler and outdoor unit at the breaker before removing access panels or touching wiring.

Steps to diagnose:

• Check breakers and switches: Verify that the furnace/air handler breaker is ON and that any service switch near the unit is also ON.
• Inspect furnace door switch: Ensure the blower door is properly installed and depressing the safety switch. An open door switch will cut power to the control board and thermostat.
• Check low‑voltage fuse: With power off, remove the furnace panel and inspect the 3–5 A blade fuse on the control board. Replace if blown, and look for shorts in thermostat wiring.
• Verify wiring at thermostat: Remove the thermostat from the wall plate and confirm that R and C wires are firmly connected and not broken.
• Measure voltage (if equipped): With power restored and the furnace door in place, measure AC voltage between R and C at the thermostat wall plate. If 24 VAC is present and the screen is still blank, the thermostat is likely defective.

When to replace: A blank screen with confirmed 24 VAC at the wall plate indicates a failed thermostat. Replace the Sensi thermostat with a compatible model.