One of the main aspects in energy conversion systems is to identify which time segment of instrumental recorded measurements allows accurate characterization of the system operation mode under a so-called "quasi steady-state". In this paper, a diagnosis procedure on an existing steam generator operating at base load in a reference power plant has been improved. The setting points for a group of key variables were considered as reference values. To assess the effects of further deviations during the time segments of operation, a set of reference variables estimated fuel overconsumption levels with regard to a theoretical zero deviation. The appropriate combination of the above mentioned regulated outputs, together with a set of suggested key modules, allowed the careful building of variants of tailor-made enhanced developments for diagnosis proposals. Finally, the contribution of this study to the assessment of compliance with environmental regulations was achieved, showing relevant savings in terms of energy consumption. (C) 2012 Elsevier Ltd. All rights reserved.