The work is devoted to the numerical investigation of unsteady regimes of the paraffin convective melting inside a closed rectangular region heated from the energy source with a constant density of the volumetric heat generation. The problem has been formulated in dimensionless transformed variables “stream function−vorticity−temperature” and solved by using a finite difference method. The main characteristics of the melting process and heat transfer in a liquid medium have been obtained and analyzed at different powers of the energy source (from 5 to 100 Watt). The influence of heat transfer from the source on the temperature distributions inside the region containing paraffin has been analyzed.