It can be generally specified that a technical system is effective and profitable if it successfully performs its function with lowest total costs (procurement costs, maintenance costs, depreciation costs etc.). Taking into consideration the life cycle of a complex technical system such as the Plomin 2 thermal power plant, total costs can be significantly reduced if due and timely attention is paid to exploitation reliability and maintainability of its subsystems. Because of the complexity of the thermal power plant itself, this research was focused on the coal mill system, and this doctoral thesis serves to present its results. For the aforementioned purpose, the effect of remedial maintenance without downtime on optimal maintenance point was examined on the example of the TE Plomin 2 mill system. Therefore, a model was developed to evaluate the contribution of remedial maintenance without downtime on optimal maintenance point from two aspects. The first aspect represents the contribution of remedial maintenance without downtime to exploitation reliability and total maintenance costs of the observed technical system, while the second aspect signifies the contribution of remedial maintenance without downtime to the optimisation of implementation time needed to perform the preventive maintenance in the case of the technical system that is observed. Consequently, it was necessary to analyse the complex technical system that incorporates the implementation of remedial maintenance without downtime with the existence of a relevant database of characteristic events, the events being the basis for establishing and statistically confirming the numerical model used for determining the optimal maintenance point.