App or thermostat indicates an open window detected; heating is temporarily reduced or stopped in the affected zone.

Note: This is usually a feature, not a fault, but can be triggered falsely.

• Check for real drafts: Confirm whether a window or door is actually open. Close it and wait 10–15 minutes to see if normal heating resumes.
• Relocate thermostat: If the thermostat is very close to a window or door, move it to a more central interior wall to avoid rapid temperature swings.
• Adjust settings: In the Netatmo Energy app, go to Settings > Advanced settings > Open window detection and reduce sensitivity or disable the feature if false detections are frequent.
• Check sensor stability: If temperature readings jump erratically, there may be a sensor issue; compare with another thermometer and consider replacing the thermostat if readings are unstable.

Persistent false open‑window detections after relocation and setting changes may indicate a defective temperature sensor; replacing the thermostat is the practical solution.