The Top Therme wellness complex in Topusko, Croatia required modernisation of four wells supplying the resort with high-quality geothermal water. The project aimed at improving efficiency and sustainability, the project replaced the old discharge system with Flexalen® pre-insulated PB-1 pipes, forming a closed-loop network for both hot (60 °C) and cold (30 °C) water. The system includes heat exchangers, two 100 m³ buffer tanks, and a cooling tower, operating daily to ensure consistent heating. Flexalen® was selected for its chemical resistance, ease of installation, and durability in geothermal environments. The upgrade enhances comfort, reduces maintenance, and supports Topusko’s vision of becoming a renewable-powered community.