What does it mean when the LCD displays 'LO' on the Rt20 RF Room Thermostat?
The LCD displays 'LO' when the battery level is low. When this happens, the thermostat will also send a command to stop the heating. After replacing the batteries, the heating will turn ON again and work at the previously set temperature. (Page 27)
From the official Bosch RT20 Rf Room Thermostat manual, page 27
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