Abstract In previous papers, two new parameters related to the performance of thermal components have been shown: the internal parameters θ (Royo and Valero 1995) and the dissipation temperature (Royo et al. 1996). When the behavior of a component of a thermal plant is impaired due to internal deteriorations, cause a modification in the behavior of another components. This implies a variation in the global efficiency of the plant. But how can this influence be quantified? This question is of utmost importance when it comes to making an energetic and economic assessment of carrying out a repair on a component, or undertaking an improvement on such a component. The aim of this paper is to show an example of the use of the internal parameters 9 and the dissipation temperatures to answer analytically this question. The example chosen is a power plant with reheating. Analytical and numerical results and their analysis are provided in the paper. For example, using this procedure, it is possible to obtain that, in the chosen plant, a diminution of 1% in the isoentropic efficiency of their high pressure steam turbine causes 0.13% diminution in the efficiency of the whole plant. The results obtained have been checked by means simulation (GATE Cycle 1995). The difference between both set of results are in all the cases lower than 4%.