A curable coating composition and the use, especially in heat exchangers, for heating and/or cooling water, in particular tap water, is described. The curable coating comprises, based on solids after curing, 35-80% by weight of an epoxysilane according to the general structure 1 and/or its hydrolysation and/or condensation products, 1: R1R2aSiR3b with R1 being 3-glycidyloxypropyl, R2 being methyl, R3 being alkyloxy or acyloxy, a being 0, 1 or 2 and b being 3−a and 20-65% by weight of a blocked polyisocyanate and optionally further components. The coating provides improved corrosion protection on aluminium surfaces, reduces limescale formation on heat exchanger surfaces and is able to withstand lateral and/or temporal temperature gradients when coated on heat exchanging surfaces.