Wall temperature response to stepwise changes in applied heat flux and/or downward liquid flow rate was investigated in a vertical heated pipe. Spatial and temporal variation of wall temperature was experimentally studied. Constant heat flux was electrically applied to a narrow thin steel foil attached to a window cut in the pipe periphery. Instantaneous foil temperature was measured from outside using IR thermography. Effect of a wide range of operational parameters, such as Re number, heat flux and location along the heating element, on the transient response of the system to the time-dependent forcing is studied. (C) 2017 Elsevier Ltd. All rights reserved.