A mono propylene glycol-based heat transfer fluid particularly tailored to central heating circuits with water circulation, and to systems with solar sensors. Provides excellent protection against freezing, and reinforced protection against corrosion of the metals present in the various circuits, whether they are of old or recent design. This relatively harmless fluid prevents the risk of intoxication in case of accidental communication between the primary and secondary circuits The inhibitors used in the formula ensure good compatibility with hard water, preventing the risks of precipitation and scaling.