Leaks in vacuum plants and systems are a big problem, especially in plants and systems where a high vacuum is necessary to perform the process. In the paper, the most commonly used methods for leak detection are investigated and processed in detail. In systems where leaks occur, it is important to locate the location of the leak in time, as well as the rate of the leak, and adequately approach the disposal problem. As part of the work, an experimental measurement was carried out in the company Centar toplinske obrade d.o.o. Measurement and testing was done on a vacuum furnace for heat treatment of materials manufactured by SECO/WARWICK. The vacuum furnace is intended for various processes of heat treatment of materials, but it is most often used for tempering materials in a vacuum where nitrogen is used as a protective atmosphere. The company's employees noticed certain damages on the treated surfaces after the heat treatment and suspected a leak in the system. Leakage detection was performed using the vacuum local method with external ready helium connected to a gun and a Leybold Phoenix Quadro leak detector with a sensitivity of 10-12 (mbar·l)/s. The method of generating a vacuum on a vacuum furnace is also described. Before starting the test, the system must be thoroughly cleaned so that contamination does not cause erroneous results. Leakage detection has shown that the leakage occurs on the underside of the vacuum chamber door and on the heater conductors at the metal-ceramic junctions.