For the sensor to work properly, it must be within range of the Tapo hub, and the hub must be within range of the main router. The Wi-Fi repeater does not allow the sensor to communicate directly with the hub via Wi-Fi, as the sensor uses low-frequency (Sub-GHz) wireless technology to connect to the hub. If you place the sensor in your cellar and the hub in your flat, make sure that the sensor is within range of the hub for effective communication.