The CHaracterizing ExoPlanets Satellite (CHEOPS) will be the first ESA Science Small Mission (S1-Mission) dedicated to the study of exo-planetary transits by means of ultrahigh precision photometry on bright stars already known to host planets. The main science objective will be to study the structure of exoplanets with radii typically ranging between 1 to 6 Earth radius orbiting bright stars. The science payload, subject of this paper, consists in one instrument including a compact on-axis Ritchey-Chrétien telescope of useful diameter of approx. 30 cm, and a single, frame-transfer, back-illuminated CCD detector. The Spacecraft is 3-axis stabilized injected on a Sun-Synchronous Orbit at a nominal altitude of 700 km and 06:00 am Local Time at Ascendant Node. The Instrument will point anti-Sun direction +/- 60°. A sunshield protects the focal plane radiator from direct sun illumination providing it with a stable thermal environment. During its orbit, the spacecraft is slowly rotated for maintaining the focal plane radiator oriented towards cold space, enabling a passive cooling of the detector to below 233 K and ensuring its thermal stability (<10 mK). This paper will present the latest evolution of the Instrument thermal design and how the thermal control was verified by test first using an early Structural and Thermal Model thermal balance test followed by the Proto-Flight Model thermal cycling and thermal balance tests. The paper will present the main outcomes of the integration and the tests including the thermal model correlation and the updated in-orbit predicted thermal performance. With the Instrument delivered to the Platform early 2018, the CHEOPS project targets a launch readiness by December 2018.