In vanadium redox flow batteries (VFB), the power of the battery is determined by the number of cells in the stack. Serial and parallel layouts are commonly adopted interactively to suit the designed power demand. The bipolar stack design inevitably introduces shunt currents bypassing into the common manifolds in the stack and thereby resulting in a parasitic loss of power and energy. During standby, shunt current and its associated internal discharge reactions can generate heat and increase stack temperature, potentially leading to thermal precipitation in the positive half-cell. This study aims to investigate the effect of shunt current on stack efficiency and temperature variation during standby periods for a 40-cell stack. Dynamic models based on mass balance, energy balance and electrical circuit are developed for simulations and the results provide an insight into stack performance that will aid in optimising stack design and suitable cooling strategies for the VFB.