The paper presents the elements of analyses of thermal system operation performed on the fundament of real values received from continuous measurement and models formulated on this data basis. The system is a part of a thermal power plant supplied from boilers and turbines cooperating with volume heat exchangers. The measurements have been recorded in heating seasons and collect several simultaneous parameters of operation. Then, the models have been formulated on the real data and in turn new values generated. The presented research elements are based on linear parametric models with the preliminary non minimal phase parametric models. The paper presents and describes simplifications introduced to system diagrams to formulate the parametric models and their operation. The characteristic for this analysis is the transfer from the presentation of physical processes towards relation between in and out parameters. MATLAB and MathCad tools are used for the calculation. The conclusions that could follow the composition of the models are important especially in the aspect of effectiveness taking into account that the real data comes from a fully controlled system which as such meets all requirements. This additional diagnostics of energy system elements lets us precise the control, minimise the loss of energy and allows for better control for the use of fuels. Moreover the formulation of prognosis of improved accuracy in comparison to the reference, which is to be worked out, would be advantageous from the point of energy business. The possibility to increase the amount of energy production from conventional fuels and biofuels, generally known of medium efficiency, can have the impact either on technology or on public appreciation for unconventional fuel