Closed valves are recurring problems in water distribution systems (WDS). Valves closed during normal exercising or by contractors during construction or system maintenance are not always reopened. The existence of a closed valve not only reduces the operation efficiency, but also can cause severe safety problems when a fire occurs. A methodology to detect closed valves using reflected transients in a full hydraulic transient analysis is presented here. A valve closure varies a pipe's flow rate and often causes an immediate change of pressure and pressure transient. If the valve closure is completed somewhat slowly, a transient with a non-harmful peak is generated but a measurable signal. The premise of this methodology is that in the WDS the reflections of the pressure wave will be altered by a closed or partially closed valve. We begin with a paper study that considers that only one valve is improperly closed. The most likely locations of the closed valve are identified by enumeration.Comparisons between computed and "measured" pressure signals are made using the root mean squared error. Measured signals are developed from numerical model results with random generated measurement errors. A hydraulic transient model based on Chen (1995) is used to compute and analyze transients. Ongoing work is investigating the effect of the number of pressure meters, valve location and valve closure rate. Further work will examine cases with multiple closed valves including optimization methods for alternative optimization algorithms, objective functions and other pattern matching approaches.