Would that be the installer who has to warranty the product or the manufacturer.  For example, you do a pipe out in polybutene which has a 25 year manufacturer warranty. As it's just behind wall linings NZBC asks for 15 years. But there a fault in the pipe and it fails after 7 years, does the installer get left with the problem? .

Pretty sure most guys are not aware of that, especially the need to retain public liability insurance well into retirement when it is least affordable. The biggest bugbear is that manufacturers dont appear to be held to the same high standard. How many times have you installed a fitting and found it cracked, split, squashed or damaged in some way and the manufacturer always says not our fault, you did it when you installed it. Now that so much stuff is being produced off shore, the fault rates are climbing with no recourse to the installer who is always the last man and gets to wear costs.