Flexible pre-insulated, self-compensating underground pipe comprising two heating pipes and two sanitary pipes. Designed for heating water (flow and return), and equipped with a sanitary hot water pipe and a pipe for the circulation loop. Corrosion-resistant transport pipe in cross-linked PE-Xa in accordance with EN ISO 15875, with yellow oxygen diffusion barrier in accordance with DIN 4726 for the heating water pipes. Thermal, elastic, CFC-free foam insulation made from cross-linked PE-X with closed microcellular structure. Minimal water absorption capacity of < 1% in accordance with ISO 2896. Insulating PE centrepiece guarantees an effective separation of flow, return, hot water and circulation pipes. Corrugated outside casing in HDPE, made in accordance with the closed chamber principle to provide high-grade protection to the piping system. 2x25x2.3, 1x28x4, 1x18x2,5, 20-20-20-13, 160, 2,58, 0,60.