If your device is not stopped, in frost protection or ECO mode, the setpoint temperature on it may have been reached. In this case, your device will heat again as soon as the room temperature drops. The open window function, if present on your device, can also shut down the heater if it detects a sudden drop in temperature. In this case, on the appliance thermostat, the window detection symbol will flash. Just press the window button to restart the heating. For more details, refer to the "Diagnostics help" section of your device.