Thermostat displays E6 and cannot detect the outdoor temperature from a heat pump or external sensor

Safety: Turn off power to the outdoor unit and furnace/air handler at the breaker before working on any wiring.

• Step 1 – Confirm your system uses an outdoor sensor: Many systems provide outdoor temperature via the heat pump control board or an external sensor. Check your equipment documentation.
• Step 2 – Inspect outdoor sensor wiring: Locate the outdoor sensor on the heat pump or near the outdoor unit. Follow its low-voltage wires back to the control board or ecobee accessory terminals. Look for cuts, corrosion, or loose connections.
• Step 3 – Verify compatibility: Ensure the outdoor sensor type (thermistor value, digital bus, etc.) is supported by your HVAC equipment and ecobee configuration. Ecobee typically reads outdoor temperature via the internet, not a direct sensor, unless integrated through specific equipment.
• Step 4 – Disable external sensor in settings: If no physical outdoor sensor is installed, go to Menu > Settings > Installation Settings > Equipment and disable any external sensor options so ecobee uses internet weather.
• Step 5 – Replace sensor if failed: If your system relies on a physical outdoor sensor and it tests open/shorted with a multimeter, replace it with the OEM sensor specified by the heat pump manufacturer.