This paper deals with a maintainability analysis of a system which consists of three subsystems. Two subsystems in the system are the same and constitute a warm standby redundant system. This warm standby redundant system and the residual subsystem are connected in series. In this paper, two repair disciplines are considered. One is a priority repair discipline and the other is a non priority repair discipline. The Laplace transform of the point-wise availability and the steady state availability for the system are derived under each repair discipline, and comparisions of the two results are made. Then the effect of the priority repair discipline on an increment of the system availability is discussed.