Thermostat screen is completely blank and HVAC system does not respond

Danger: HVAC systems contain high voltage. Turn off power at the breaker before opening any panels.

• Step 1 – Check breakers and furnace switch:
  • Verify that the furnace/air handler breaker is ON and the service switch is not off.
• Step 2 – Inspect furnace control board fuse:
  • Turn off power, open the blower compartment, and locate the control board.
  • Check the low‑voltage blade fuse; replace if blown with the same rating.
• Step 3 – Verify R and C voltage:
  • With power on, measure AC voltage between R and C at the furnace board and at the thermostat wall plate; should be ~24VAC.
  • If present at the board but not at the thermostat, repair or replace the thermostat cable.
• Step 4 – Check thermostat connections:
  • Ensure R and C wires are firmly connected at the thermostat base.
• Step 5 – Replace thermostat if powered but dead:
  • If 24VAC is present at the thermostat but the screen remains blank, the internal power circuit or display is likely failed; replace the thermostat.