The Mezőberény Geothermal Demonstration Plant is a geothermal heating plant with two wells, belonging to the City of Mezőberény. It is located in the South-East part of Hungary in the middle of Békés country. Geothermal potential of the Pannonian Basin and its utilization has a long tradition in Hungary. The main aquifers are carstified Mesozoic rocks and Pannonian sandstones. However, the injection into the sandstones has a relatively short history in Hungary. The Mezőberény geothermal site was constructed in 2011-2012, with the aim to utilize the geothermal potential in the Békés Basin for district heating. The system consists of one production well (B-115) with a depth of 2’003 m, and one reinjection well (K-116) with a depth of 2’001 m. After a three-weeks operation, injectivity radically dropped, which lead to a stop of the operation. In 2017, a mechanical and chemical cleaning campaign was carried out to remove clogging material, but a long-term solution for injectivity increase has not been found yet (Siklósi, 2017).