Numerical simulations of the heating repartition effect on the boiling flow in vertical tube are performed using the commercial CFD (Computational Fluid Dynamics) package FLUENT. The Eulerian multiphase flow framework model was applied to describe the phase interactions. User-Defined Functions (UDFs) are provided to compute the wall heat transfer and the inter-phase heat and mass transfer. Two different configurations of the bubble pump are considered: Total and partial heating of the pump tube. Preliminary calculations are performed with pure water as working fluid. The results presented and discussed in this paper concern the void fraction distribution, flow regime repartition, liquid-vapor velocities arrangement and temperature profiles. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.