This paper presents an approach to formally verify the detection capability of a system hang detector. To achieve this goal, an abstract formal model of a typical Linux system is created to thoroughly exercise all execution scenarios that may lead to hangs. The goal is to expose cases (i.e., hang scenarios) that escape detection. Our system model abstracts the basic hardware (e.g., timer, hardware counter) and software (e.g., processes/threads) components present in the Linux system. The model enables: (i) capturing behavior of these components so as to depict execution scenarios that lead to hangs, and (ii) evaluating hang detection coverage. Explicit-state model checking is applied to reason about system behavior and uncover hang scenarios that escape detection. The results indicate that the proposed framework allows identification of corner cases of hang scenarios that escape detection and provides valuable insight to developers for enhancing detection mechanisms.