Home Assistant Thermostat Heating circuit - bosch-thermostat/home-assistant-bosch-custom-component GitHub Wiki
Bosch name for HA climate component is heating circuit.
Current temperature
In some situations there are no current_temperature. It is because your module doesn't provide room temperature for Heating Circuit. Technically then HC is reporting -3276.8 and it means faulty/no sensor.
This is the case when the thermostat is installed inside the heater, and not in the reference room.