CONTROL DEVICE OF WATER HEATER

摘要

PURPOSE:To prevent a dangerous over-combustion and provide a decreased number of component elements by a method wherein resistor elements for providing a reference voltage in a comparator for adjusting temperature and sensing excessive increasing of temperature are separately arranged. CONSTITUTION:When a thermistor 21 is troubled in its breaking line, a reversed input of a convertor 36 for detecting increased temperature and broken line is applied with a voltage having a partial voltage ratio between resistors 22 and 23. This voltage becomes higher than that applied when the thermistor 21 is not broken. When an output of a microcomputer 38 is at a high level, a reference voltage of the comparator 36 becomes high. However, this reference voltage is lower than a voltage applied to the reversed input of the comparator 36. Therefore, the output of the comparator 36 is at a low level and the microcomputer 38 senses the disconnection of the thermistor 21. An input port of the microcomputer 38 for use in inputting an output of the comparator 36 performs a discrimination of the input in synchronization with the output of said output port.