TFA Dostmann 30.3016.01.IT Manuel D'utilisation page 59

Display "---"
Incorrect display
rechargeable batteries!)
 Restart the transmitter and temperature station as
per the manual
 Choose another place for the transmitter and/or the
temperature station
 Reduce the distance between the transmitter and
the temperature station
 Check if there is any source of interference
 Change batteries
58