It is already well known that Loop Heat Pipes (LHPs) are able to transport heat over long distances, through flexible, small diameter tubes and against high gravitational heads. The existing experience of the conventional Heat Pipe history says that during the time some amount of non condensable gases (NCG) can be generated inside the closed system with the working fluid inside. It was shown in many previous publications how sensitive conventional heat pipes with composite wicks are on the presence of NCG. In spite LHPs are already widely applied in spacecraft, the NCG issue was not studied yet. The paper describes the work aimed at LHP operation study when NCG are injected.The experimental study of the LHP operation was performed. The LHP response on NCG injection with some increments was monitored in order to register any changes of the LHP performance. The End of Life (EOL) NCG amount in the ammonia LHP was calculated. The way of theoretical analysis is discussed in the paper.Hydrogen and Nitrogen are the most common gases which can be generated in the ammonia-stainless- aluminum envelope, so they were chosen as simulate the generated NCG. The performance history of the LHP prior, during and after injection discussed in details as well as the change of LHP conductance.