Why are plomyCLICK fittings to be installed with plomyPEX pipes and/or plomyLAYER pipes only?
Because the plomyCLICK system is warranted by the manufacturer of all its component parts. If you use plomyCLICK fittings with pipes different from those recommended by the manufacturer, the manufacturer will not be able to warrant the successful performance of the whole system. The combination of products manufactured by different companies in the same installation would invalidate the warranty of the plomyCLICK system. The reason is that in that case you would not be installing the plomyCLICK system as such – instead, you would be installing plomyCLICK fittings with some other pipe.