When fitting an Aquadial scale inhibitor, which side should the check valve be fitted? As the instructions state there must be no possibility of hot water transfer back through, which could happen in my mains pressure thermal store if I turned off the main stop cock for any reason. And I'm assuming I ought to have a check valve before the unit to prevent back flow of inhibitor chemicals, this sort of implies I need to check valve both sides. Anyone got any advice on the usual practice for these?