The aim of this paper is to define and characterize a new parameter, the dissipation temperature. When a thermal plant component displays an internal deterioration (intrinsic malfunction), its performance gets worse. This fact is reflected in a variation of the internal parameters that describe its behavior (isentropic efficiency, effectiveness, pressure and/or temperature ratios, parameter theta [1]). On the other hand, the remaining components of the plant may be affected (by induced malfunctions) because they are working under different operating conditions with respect to the rated ones. The knowledge of variations of the internal parameters in each component of a thermal plant does not suffice to determine their performance state under these new conditions. Additional information is needed. The dissipation temperature, defined as dh/ds when a malfunction occurs, can supply it as is explained in this paper. Moreover, three interesting applications of the dissipation temperature are shown: description of an energy system when a malfunction occurs; assessment of the importance of an intrinsic malfunction in a component; and the analysis of the influence of a malfunction on the exergetic efficiency of a component.