Mean times to failure are fundamental indicators in reliability and related fields. Here we focus on the conditional mean time to failure defined in a semi-Markov context. A discrete time semi-Markov model with discrete state space is employed, which allows for realistic description of systems under risk. Our main objective is to estimate the conditional mean time to failure and provide asymptotic properties of its nonparametric estimator. Consistency and asymptotic normality results are provided. Our methodology is tested in a real wind dataset and indicators associated with the wind energy production are estimated.