Thermostat screen is completely blank and unresponsive

Safety: Turn off power to the furnace/air handler at the breaker before opening panels. Use a multimeter only if you are comfortable working around low-voltage circuits.

• Step 1 – Check breakers: Verify that the furnace/air handler breaker is on and not tripped. Reset if necessary.
• Step 2 – Inspect furnace fuse: Open the furnace panel and locate the low-voltage 3A fuse on the control board. Replace if blown with the same rating.
• Step 3 – Verify 24V at furnace: With power on, measure between R and C on the control board. You should see ~24 VAC. If not, the transformer or board may be faulty.
• Step 4 – Verify 24V at thermostat: Remove the ecobee and measure between R and C on the backplate. If there is no voltage but there is at the furnace, the thermostat cable is damaged and must be repaired or replaced.
• Step 5 – Replace thermostat if powered but dead: If 24V is present at the backplate but the ecobee remains blank, the thermostat is likely defective and should be replaced.