Thermostat displays E6 and may not control auxiliary heat or heat pump correctly.

Safety first: Turn off power to the HVAC system at the breaker before changing wiring.

• Step 1 – Verify system type: In the thermostat's installer or advanced settings, confirm that the system type matches your equipment (e.g., heat pump with electric backup, heat pump with gas furnace, or conventional furnace/AC).
• Step 2 – Check O/B wiring: Remove the thermostat and verify the reversing valve wire (usually orange) is connected to the O/B terminal. Confirm the thermostat is configured for the correct reversing valve operation (O for cooling, B for heating) per your Carrier heat pump documentation.
• Step 3 – Verify Aux/Stage wiring: Ensure W2/Aux is wired to the auxiliary heat relay on the Carrier air handler or furnace. Tighten any loose connections.
• Step 4 – Run system test: Use the thermostat's built-in system test (if available) to energize each stage and verify proper operation. If E6 persists, reset the thermostat to factory defaults and re-run the guided setup.
• When to call a pro: If you are unsure of your system configuration (dual fuel, multi-stage, etc.), have a Carrier technician confirm and program the thermostat correctly.