The discredibility can be detected either by installing additional sensor or by software detection. The additional sensor is not suitable due to increased cost of the boiler. Therefore the extended function of the control loop based on model of behavior of the sensor is the efficient solution. The proposed model-based sensor discredibility detection method is based on the model of the control variable sensor: The main advantage of such a solution is that all necessary data is already available from the technological process. The general requirement for successful application of the method is to design a so-called objective function. In terms of sensor discredibility detection, this function is called a residual function or a residuum e(t) (the difference between the output of the sensor model and the real sensor output). During discredibility detection, the residuum is minimized via sensor model parameter adaptation. Basically, if the change in the sensor model parameters exceeds the limit of the tolerance range, the operator is informed to perform any further measures or precautions.