Problem is that given the shelter they get from the workings of the Sale of Goods, the manufacturers see whatever they spend on installer incentives, etc as marketing expenses, not an essential cost of staying in business! In the end, the more installers who think 'Biasi' (or 'Vokera'!) when selecting a boiler to recommend, the more successful that manufacturer becomes - up to a point. That point is when the boiler in question gets some REALLY bad publicity (eg. Potty Suprima / BBC-TV Watchdog) or is consistently bad-mouthed in the trade (Ideal Eyesore). Then they simply change the name and soldier on: 'Barcelona' becomes '100/4' and the customer has no idea what's inside the casing.
You say that you've been trying to get installers to raise their game since forever. I wish I could think of effective ways, too!!
The other great irony is that for boilers (and cars, and everything else 'consumed' by our great civilisation) there's hardly any economic incentive to raise quality of manufacture or installation so that the products actually last longer. If you try to make a car that lasts 20 (or 50!) years, you'll go bust.