This paper presents a summary of our most recent advances in Thermoeconomic Diagnosis, developed during the last three years, and how they can be integrated in a zooming strategy oriented toward the operational diagnosis of complex systems. In fact, this paper can be considered a continuation of the work presented at the International Conference ECOS'99 in which the concepts of malfunction (intrinsic and induced) and dysfunction were analyzed in detail. These concepts greatly facilitate and simplify the analysis, the understanding, and the quantification of how the presence of an anomaly, or malfunction, affects the behavior of the other plant devices and of the whole system. However, what remains unresolved is the so-called inverse problem of diagnosing, i.e., given two states of the plant (actual and reference operating conditions), find the causes of deviation of the actual conditions with respect to the reference conditions. The present paper tackles this problem and describes significant advances in addressing how to locate the actual causes of malfunctions, based on the application of procedures for filtering induced effects that hide the real causes of degradation. In this paper a progressive zooming thermoeconomic diagnosis procedure, which allows one to concentrate the analysis in an ever more specific zone is described and applied to a combined cycle. In an accompanying paper the accuracy of the diagnosis results is discussed, depending on choice of the thermoeconomic model.