Fig. 3 depicts the control loop where the controller was used for temperature of heated water regulation. PI controller adjusts fuel feed rate regulating the boiler heat input and thus affecting the water temperature. A simple thermo mechanical steady-state model was created and with help of data from previous experiments, a simple mathematical model in the form of linear differential equations was estimated. Based on the estimated model the parameters of the PI controller were determined using Compensation of Dynamics method [9].