E8 error appears when using heat pump mode; auxiliary heat may not engage correctly

Safety: Turn off power to indoor and outdoor units at the breakers before working on wiring.

• Verify system type: In the Kasa app, confirm the thermostat is configured for a heat pump system and that the O/B reversing valve setting matches your equipment (energized in heating or cooling).
• Check O/B wiring at thermostat: Ensure the O/B wire is connected to the correct terminal and firmly clamped.
• Check at air handler/furnace: Confirm the O/B wire from the thermostat is properly landed on the heat pump control terminal strip.
• Inspect cable: Look for damage or shorts in the thermostat cable between thermostat and air handler.
• Test operation: Restore power and switch between Heat and Cool modes. Listen for the outdoor unit’s reversing valve click. If E8 persists and the valve never actuates, the thermostat O/B output or the outdoor unit’s control board may be faulty.
• Resolution: Replace the thermostat if wiring and configuration are correct. If problem remains, have a technician test the heat pump control board and reversing valve coil.