Efficient maintenance of heavy machinery is of utmost importance in geothermal power plants. Icelandic geothermal power plants are striving to domesticate its maintenance procedures to decrease foreign dependency. This study shows which problems are most frequently observed in turbines at the largest geothermal power plant in Iceland, Hellisheidi. It also describes how the turbines are monitored and how such monitoring effects the maintenance planning. The purpose of this study is to describe and analyse the methods used when planning turbine maintenance in a practical manner as they have diverted from original recommendations from the turbine manufacturer. The results can then be used by other power plants when planning the turbine maintenance. Findings show that scaling on first step of the turbine, bearing condition, blade and diaphragm condition is monitored most closely. The frequency of major maintenance on most important parts on the turbine is also shown to be between 4 and 8 years. Erosion is a problem in need of a sharp attention as it causes wear on parts and requires intrusion into turbines for inspection while producing no output. How Reykjavik Energy, the owner of the plant studied, is attempting to solve the most prominent problems is then described. This article depicts how turbine monitoring is currently used and how it affects maintenance planning at the Hellisheidi geothermal power plant, operated by Reykjavik Energy, Icelands largest geothermal energy utiliser. (C) 2015 Elsevier Ltd. All rights reserved.