The role of equipment maintenance in manufacturing becomes important. As a method of overcoming this problems, diagnostic expert system has been introduced. If such a system is, however, based on the troubleshooter's knowledge, many difficult cases are occured in the real process of diagnosis using that kind of system. This paper suggests to use the designer's knowledge for diagnosing the malfunctions of production equipments. To do that, a method of knowledge represen-tation is also proposed, which is based on the concept of boundary factors. In addition, the disorder propagation in considered. As a results, one can simplify the process of reasoning and inspection.