Abstract: A method and a valve apparatus for surveying the condition of a control valve. The position of the valve (101) is adjusted by means of an actuator (103) controlled by an electropneumatic positioner (104) and operated by means of pressure medium. The operation of the valve is monitored by sensors (109, 110, 107) that read the readings from the control signal, the input pressure of the positioner, the difference between the input and output pressure of the actuator, and the position of the valve. A fault causing a deviating reading will be located by using the readings given by the sensors and deduction rules stored in the microprocessor of the actuator. In an initial situation, when the valve is in balance state, the readings given by the sensors are stored at least from the control signal, valve position and the difference between the input and output pressure of the actuator. When the operation is continued, the readings given by the sensors are compared with the readings of the initial situation.