A valve that can be actuated by a position controller via a drive, wherein the position controller has a housing and is fastened to the valve by the housing. A first temperature sensor and a second temperature sensor are attached on or in the housing. As a result of the position of both sensors, the temperature measured using the first temperature sensor is more readily influenced by the valve and the temperature registered by the second temperature sensor is more readily influenced by the environment. If a gas leak occurs in the valve, a temperature difference occurs that is evaluated for diagnosis of a leak. The diagnostic system is particularly easy to minor implement with minimal effort.