The disclosed invention concerns a method for installing and operating a thermal well (110) heat carrier transport system (100). A first flexible tubular part (120) is provided into and along a thermal well (110), a second flexible tubular part (130) is provided into the first flexible tubular part (120) and a third open ended tubular part (140) is provided into the second flexible tubular part (130). During installation and operation an installation liquid and heat carrier, respectively, is provided into the second flexible tubular part at an overpressure sufficient to press the first flexible tubular part (120) radially against the inner all of the thermal well (110) in all radial directions. The invention also concerns a system.