If the AC•THOR / AC•THOR 9s displays the error message 102, it means that the function of domestic hot water assurance is active, but no temperature sensor has been connected or activated yet. To resolve this error, connect the sensor to the AC•THOR and activate it through the display. To do this, click on Settings (gear symbol), scroll to the 'Sensors' section, and select it. After that, you will see the serial number of the connected sensor and its current temperature on the display. Click once on this line. Now, the sensor number will be displayed to the right of the shown temperature. This means that this sensor is now active. Finally, save the setting.