This paper describes three diagnostic methods for use with industrial processes. They are measurement validation, alarm analysis and fault diagnosis. Measurement validation means consistency checking of sensor and measurement values using any redundancy of instrumentation. Alarm analysis is the analysis of multiple alarm situations to find which alarms are directly connected to primary faults and which alarms are consequential effects of the primary ones. Finally, fault diagnosis is a search for the causes of and remedies for faults. The three methods use multilevel flow models (MFM), to describe the target process. They have been implemented in the programming tool G2, and successfully tested on simulations of two processes.