E07 displayed and thermostat cannot detect any HVAC system (no R/C voltage sensed)

Danger: HVAC equipment contains high voltage. Only access the furnace/air handler control compartment if you are comfortable and power is off.

• Step 1 – Confirm HVAC power:
  • Check that the furnace/air handler switch is ON and breakers are not tripped.
  • Reset any tripped breaker and recheck.
• Step 2 – Inspect furnace control board fuse:
  • Turn off power to the furnace.
  • Open the blower compartment and locate the control board.
  • Look for a small automotive‑style blade fuse (typically 3–5A) on the board.
  • If blown, replace with the same rating and investigate for shorts in thermostat wiring.
• Step 3 – Check R and C voltage:
  • With power restored, measure AC voltage between R and C at the furnace board; should be ~24VAC.
  • If present at the board but not at the thermostat, the cable or connections are faulty.
• Step 4 – Verify thermostat connections:
  • Ensure R and C wires are firmly attached at both the furnace board and thermostat wall plate.
  • Repair or replace damaged thermostat cable as needed.
• Step 5 – Replace thermostat if sensing circuit is bad:
  • If 24VAC is present at the thermostat terminals but E07 persists, the internal R/C detection circuit on the thermostat is likely defective.
  • Replace the thermostat.