And what makes you think I don't hold the correct qualifications, mains pressure hot water systems have been used in the EU for many many years and are installed by DIY home owners without any legislative problems, having had these systems for so long they and others fully understand the need for pressure relief valves and pressure valves on the water main, explosions! there are no reported instances of explosions in the UK or EU either that I have heard first hand about, lots of I "was told about" of an explosion nonsense, mains pressure domestic hot water systems are the norm in the EU, but unfortunately the UK have been so far behind with vented cylinders for so long UK plumbers are scared stiff of something new and will invent problems to ensure they get the job of installing, I have to say that the responses are so typical of the UK plumber that frequents these page's it's painful, why don't one of you try to answer the question instead of being obstructive.