Furnace control board shows E0 and will not start a heating cycle

Safety first: Turn OFF power to the furnace at the service switch and the breaker. Verify power is off with a non-contact voltage tester before touching any wiring.

• Check the furnace door switch: Ensure the blower compartment door is fully closed and engaging the door safety switch. An open switch can cause communication or idle codes.
• Inspect low-voltage fuse: Locate the 3A or 5A blade fuse on the Kelvinator control board. Remove and visually inspect. If blown, replace with the same rating only. If it blows again, there is a short in the thermostat or low-voltage wiring.
• Verify thermostat wiring: Confirm that the R and W (and C if used) wires are firmly attached to the correct terminals on both the thermostat and the Kelvinator control board. Look for bare copper touching other terminals or the furnace chassis.
• Check wiring harnesses: Gently press all multi-pin connectors into the control board until fully seated. Look for corrosion, bent pins, or partially unplugged connectors.
• Power cycle: Restore power, then turn the thermostat to HEAT and raise the setpoint. Observe if the E0 clears. If the code persists and all wiring is correct, the control board may be defective.
• When to call a technician: If you suspect a bad control board or damaged harness and are not comfortable with low-voltage diagnostics, contact a qualified HVAC technician.