Solar thermal collector comprising a plurality of parallel vertical tubes, connected to each other by one upper horizontal tube and one lower horizontal tube through which a heat carrying fluid flows, a glass surface that covers the parallel vertical tubes, the upper horizontal tube and the lower horizontal tube, and a dissipating device installed in an upper part of the solar thermal collector, the heat dissipating device comprising a thermostatic valve, a heat exchanger and a return pipe, wherein the thermostatic valve is housed in the upper horizontal tube, the thermostatic valve and the heat exchanger being connected to a pipe by way of an inverted U-shaped tube provided at a greater height than the inlet to the heat exchanger, such that, under normal working conditions, energy losses by heat transfer by convection from the thermostatic valve to the heat exchanger are interrupted.