This error is indicated when requesting a dynamic simulation. The simulation cannot be started because of the 'unconnected boiler temperature'. The boiler still needs to be supplied with an appropriate setpoint temperature (e.g. heating curve).
This base circuit indicates that the 'base circuit is not assigned to a zone' when requesting a dynamic simulation. Currently, the software doesn't know in which building zone the radiator must drop its heat. Before running a simulation, the radiator must be assigned to the right zone (see building and loads library).