Fast recovery silicon (Si) power diodes, having radiation induced recombination centres, operating under forward bias at large current densities and high temperatures, have been studied in a detailed way, both experimentally and with the help of device simulation Medici package. The comparison of the dynamic I-V characteristics with the results of numerical simulations is possible only when all the specific features of the measurement set-up are taken into account in the simulations. Such evaluation of the electro-thermal numerical model of the diode under experiment combined with the electro-thermal model of the experimental set-up as the boundary condition for Medici simulation is being presented. The main issue is the definition of the thermal boundary conditions.