Abstract: A radiator valve for preventing water from leaking out of a radiator when the radiator is detached from its hot water supply. The radiator valve includes a tubular housing with a lumen and opposite first and second ends. A ball valve is rotatably mounted in the lumen of the tubular housing to substantially block passage of fluid through the lumen of the tubular housing. The first end of the tubular housing is designed for attachment to a fluid opening of a radiator to fluidly connect the lumen of the tubular housing to the fluid housing of the radiator. The second end of the tubular housing is designed for removable attachment to a fluid supply outlet of a fluid supply conduit to fluidly connect the lumen of the housing to the fluid supply conduit.