Preassembled pump group for fixed-point regulation and circulation of mixed fluid. Allows the circulation of the thermal fluid, coming from the primary circuit, by keeping the temperature at a pre-set value (fixed-point) through the help of a mixing valve and a fixed-point actuator with integrated controller and probe. It is used in heating systems in general and radiant panel systems. The group is composed of a pump, flow/return shut-off valves, motorizable mixing valve, fixed-point actuator, flow/return temperature gauges, anti-thermosiphon check valve, thermal insulation. In this group the differential by-pass valve can be installed only externally. The group is reversible (the flow line can be exchanged with the return line).