Precipitation-hardened Cu-Cr-Zr will be used in heat-sink components in the Iter tokomak. After irradiation it will not be possible to test the mechanical properties of Cu-Cr-Zr using conventional, large-scale, techniques and methods requiring reduced sample sizes will have to be used. Spherical nano-indentation is one such method. In this work, Cu-Cr-Zr has been heat-treated at different temperatures to vary the Cr precipitate size and spacing. Spherical nano-indentation using multiple tip radii was then used to produce stress-strain curves for all samples, from which values of yield pressure were calculated. It was found that there was a strong indentation size effect in yield pressure values, however at higher indentation strain the response became size-independent at tip sizes above ~10 µm. This supports the theory that at the initiation of plastic deformation the ISE is due to dislocation source activation but in later stages of it is the interaction with intrinsic material length-scales that dominates the measured mechanical strength.