Thermostat displays E17 and cannot read the outdoor temperature from an external sensor or internet source.

Safety first: Isolate power before working on any wired outdoor sensor connections.

Steps to check:

• 1. Determine source type: Confirm whether the thermostat uses a physical Baxi outdoor sensor or internet-based weather data.
• 2. For wired sensors: Inspect the outdoor sensor and cable for physical damage, water ingress, or loose terminals. Test sensor resistance with a multimeter and compare to Baxi’s chart.
• 3. For internet weather: Ensure Wi‑Fi and cloud connectivity are working and that your location is correctly set in the Baxi app.
• 4. Reboot and reconfigure: Power-cycle the thermostat and re-enter location or sensor settings.

When to call a professional: If a wired sensor tests faulty, replace it with a genuine Baxi outdoor sensor. If wiring and sensor are good but E17 persists, the thermostat input may be defective.