Abstract: The scale-inhibiting agent used is a combination with a synergistic effect of at least 50% by weight of salified polymers of ethylenic acids, chosen from polymaleates, polyacrylates, polymethacrylates, maleateacrylate copolymers, acrylate-methacrylate copolymers, acrylate-methacrylate-itaconate terpolymers, and mixtures of these substances, and at most 50 wt. % aliphatic polyamines with the formulaR--NH -(CH.sub.2).sub.3 ].sub.n NH.sub.2wherein R represents an aliphatic radical having 12 to 18 carbon atoms and n can be an odd or even whole number between 1 and 6, the percentages being based on polymers and polyamines in the dry state. These percentages are preferably 5 to 15 wt. % aliphatic polyamines per 95 to 85 wt. % polymers.