This paper documents the fundamentals of heat storage by melting a phase-change material inside a cylindrical enclosure with a vertical heated pipe on its axis. The phenomenon is studied analytically and numerically. The analysis consists of the scale analysis of the early stages of natural convection in the liquid, and an analysis of the entire duration of the melting process. The numerical simulations cover the entire process, and validate all the features predicted by theory. (C) 2014 Elsevier Ltd. All rights reserved.