Abstract: A liquid heating device particularly adapted to the heating of sealed bottles containing liquids which are maintained in sterile condition until used, such as dialysates and the like. The device employs sealed bottles having a temperature sensitive element in intimate contact with the liquid being heated, which changes to a predetermined color and hue as the desired temperature is obtained. This color is compared with a color standard using a single source of light which is reflected against the indicator and the standard. The light reflected from these elements is photoelectrically compared, and the operation of the heating element is interrupted when a match is made. An independent timer interrupts said operation in the event of a failure of the photoelectric comparison.