The Object-Oriented (O-O) approach has been recently used in the industrial automation to design logic control systems, thanks to the features of specification languages (e.g. UML) that can help to describe event-based behavioral requirements. In this paper, we aim to formalise an O-O framework for the design of modular logic controllers, in which faults occurring in the plant can alter the behavior of closed-loop system. Given the formal model of the system in terms of Kripke structures, it is possible to verify with model checking that even in case of faults the system do not violate given safety and liveness properties. Moreover, we will consider the case in which an O-O logic controller is refined applying the so-called “design-byextension” mechanism, in which case it is important to verify that the fault tolerance property is inherited by the refined system.