In this paper we investigated a replacement model with two types of repairs. Repairs are classified into minimal and perfect repair. An operating unit is completely replaced whenever it reaches age τ(τ> 0) at a cost c,(planned replacement). If it fails at age t <τ, it is either restored by a entire unit with probability d(t) at a cost c2(perfect repair), or it undergoes minimal repair with probability p(t) = 1 - p(t) at a cost c₃. After a planned replacement, the procedure is repeated. The aim of this paper is to find conditions where the optimal planned replacement period τ^(*) which minimizes the total long-run expected cost per unit time can exist.