Trouble-free operation of the main equipment of heat power plants is determined by the performance reliability of condensing units. High air density of the vacuum system provides cost-effective and reliable operation. One of the reasons that causes an increase of the exhaust steam pressure compared to the standard pressure, in addition to contamination of the condensers cooling surface, is the high amount of air inflow through vacuum system leakiness. Exceeding the amount of atmospheric air inflow into the vacuum system above the standard value, both reduces the available heat energy and make worse the deaeration capacity of the condenser. This results in saturation of the full-flow condensate with oxygen and intensification of corrosion processes. Various methods varying in both cost and efficiency are used to find air inflow location. Nowadays, the issue of choosing a method to detect even the most insignificant air inflow location of the vacuum system of a steam turbine remains open. In the current study, the authors have used the thermal-imaging method to detect air inflow location due to local hypocooling, and the ultrasonic method, which is based on the detection of ultrasound created by gas flows. The authors have proved the necessity to use several different in concept methods to find leakage locations in a vacuum system. It is established that traditional methods to find vacuum system leaks do not allow to eliminate excess leaks. In-service monitoring confirms 87 % reduction of the amount of vacuum leaks. The studies show high efficiency of sharing both thermal imaging and ultrasonic methods to detect air inflow location in a vacuum system. According to the operating conditions of the available equipment, as well as the personnel qualifications, the results obtained make it possible to choose the most optimal way in terms of financial and time expenses to find vacuum leakage location in the vacuum system of a steam turbine.