Water heating and boiling, Photo 3 of 5. An immersion heater is used to heat and boil water. In this sequence, the heater is put into the water at room temperature (Photo 1). Shortly, small bubbles start to appear on the heater element (Photo 2). Then the number of bubbles increases and they grow in size (Photo 3). With continued heating, bubbles start detaching from the heater and rise to the top, while new bubbles appear on the heater (Photo 4). Finally, during active boiling, larger bubbles appear and rise up very rapidly (Photo 5).