The pressure derivative method is one of the most significant developments in the history of pressure transient analysis (PTA). PTA results that would otherwise be difficult to interpret can have a clear and characteristic pressure derivative. The application of this technique in groundwater, coalbed methane, mineral exploration and oil and gas wells has been widespread. However application to geothermal wells is still very limited. The usefulness of the pressure derivative method is demonstrated in this study. Despite the challenges of geothermal wells it remains a key diagnostic tool to determine the processes taking place during a test and therefore the models to apply during analysis. Three common issues which affect PTA in geothermal wells are: (1) downflows, (2) slow valve closing and (3) two-stage pump shut-down. Issue 1 involves downflows of fluid from a higher permeable zone to a deeper one of lower pressure. Issue 2 is the inevitable delay when manually opening or closing a valve to control the flow rate during a test. Issue 3 of two-stage pump shut-down occurs when using pumps for injection and not all pumps cease injection at the same time. Both Issues 2 and 3 effectively produce non-zero flow early in the PFO and can look similar. For each issue some real examples are given. The characteristic anomalies these issues produce in a derivative plot are presented. Some analyses and discussion are presented of the extent to which these issues affect the results obtained for permeability (k) and skin factor (s) by treating these as standard analyses. (C) 2015 Elsevier Ltd. All rights reserved.