Just for others reading this, I think it is only if you put the system onto heating the water at the higher than normal temperature that it takes priority over the central heating. Normal water heating takes place alongside the central heating - at least that's how mine works.
Hi Well sitting in new van at Wagtail country park near Grantham. Pick it up Wednesday was worried about heating but been getting to hot so should do. Been trying to get use to Electronics. Happy Caravanning Monty