Abstract: The invention relates to a heater (1) with electrical heating elements (15-18) for waterbeds (2), which is arranged between a bed frame (4) and a safety film (5), and which controls the temperature of a metal plate (11) placed under the safety film (5) of a waterbed core (9) lying thereupon, wherein the heating elements (15-18) are connected in a heat-conducting manner with the bottom side (11a) of the metal plate (11) in a flat casing (14) via a readily heat-conducting layer (27). The object of the invention is to provide a heater that consistently prevents the metal plate (11) from overheating, and ensures a reliable control of the waterbed core (9) at varying heat transmission conditions.