The aim of the present study is to determine the efficiency of the power plant boiler steam C3 Cape deer and to evaluate the impact of it. We chose to calculate the return by the empirical formula of Martin which is based on two important parameters which are the temperature at the exit of the chimney and the ambient temperature. The calculation of these efficiencies allowed us to make comparative studies with data from the manufacturer and we have detected anomalies. On this basis we made a number of recommendations for improvement of the groups in normal, the application will lead to an optimization of the real exploitation of groups and a performance improvement. We gave various reasons for poor performance of steam generators and recommendations that can be used both in production efficiency on compliance with operating instructions. Solutions have been proposed after diagnosis with particular emphasis on compliance with operating instructions and maintenance schedule.