Training is another industry, with high powered sales people feeding the punters . It seams to work. However the plumbing / heating game has changed massively over the years. Were the plumber was involved with all types of pipework material for water, air, soil and waste, roofing in zinc, lead, copper, glazing, solid flue, oil, gas, warm air ducting, Guttering with various materials. The list goes on. Now it seems a large number carry the badge for connecting to a 15 mm main supply with a glorified Ascot on the end of it to heat the water and house, using the equivalent of hose and jubilee clips to transport the fluids. I am of the opinion that these modern methods will create plenty of poorly paid installation / repair/maintenance work for plumbers in the future. However those who specialise in areas within the trade are still having it off. Solar, solid fuel stoves, heat pumps, metal roofing and more are areas where good money can be earn't and they will be targeted when plumbing training reaches saturation point. The problem being you can not stop people from dreaming. Good Luck