Preassembled pump group for the circulation and temperature control of the water returning to solid fuel heat generators (logs, pellet, woodchips). The group is used when the generator is not equipped with a built-in pump: the group pump performs the function of system circulator and, together with the valve, anti-condensation recirculation. The group connects the solid fuel generator to the manifold or the inertial storage or directly the system. By means of the thermostatic sensor or the built-in fixed-point actuator, it keeps the water temperature, returning to the boiler, above a set value. This function allows to reduce the condensation of the combustion flue gases which causes the following problems: encrustations and deposits on the thermal exchange surfaces between the gases and the system water, corrosion and fire risk, efficiency and life reduction of the generator. The group is composed of a pump, flow/return shut-off valves, anti-condensation thermostatic mixing valve with fixed setting (15G.DN25) or mixing valve with fixed-point actuator (20G.DN25, 19G.DN32), flow/return temperature gauges, anti-thermosiphon check valve, thermal insulation. In these groups the differential by-pass valve can be installed only externally. All the groups are reversible (the flow line can be exchanged with the return line).