Antifreeze for central heating systems. A concentrate based on mono ethylene glycol, specially designed for the protection against freezing of thermo-siphon central heating systems, or those equipped with a circulation pump. It contains organic inhibitors which prevent corrosion of pipework and radiators, as well as of various metals present in the systems (steel-brass). Its new package of additives is free from borax (sodium borates), and ensure optimum protection of the systems.