In some fields of industrial automation, such as nuclear power plant (NPP) industry in Finland, thorough verification of systems and demonstration of their safety are mandatory. Model checking is one of the techniques to achieve a high level of reliability. The goal of this paper is practical: we explore which type of model checking - either explicit-state or symbolic - is more suitable to verify instrumentation and control (I&C) applications, represented as function block networks. Unlike previous studies, in addition to the common open-loop approach, which views the controller model alone, we consider closed-loop verification, where the plant is also modeled. In addition, we present a procedure to translate block networks to the language of the SPIN explicit-state model checker.