Melting of a phase change material assisted by a thermosyphon inside a two dimensional rectangular domain is numerically investigated. The PCM used is n-eicosane and the thermosyphon is made of copper. The working fluid is water. The fill ratio of the working fluid (water) is taken to be 50%. A lumped model is used for the simulation of transient operation of the thermosyphon and enthalpy-porosity method is employed for numerical simulation of melting of PCM. The effects of inclusion of multiple heat pipes on the melting of the PCM inside the enclosure is studied. Simulation results indicate that the addition of heat pipes enhances the performance of latent heat thermal energy storage system only upto a certain extent. © Published under licence by IOP Publishing Ltd.