Methods of and systems for performing leak checks of gas-phase reactor systems are disclosed. Exemplary systems include a first exhaust system coupled to a reaction chamber via a first exhaust line, a bypass line coupled to a gas supply unit and to the first exhaust system, a gas detector coupled to the bypass line via a connecting line, a connecting line valve coupled to the connecting line, and a second exhaust system coupled to the connecting line. Methods include using the second exhaust system to exhaust the connecting line to thereby remove residual gas in the connecting line that may otherwise affect the accuracy of the gas detector.