The purchaser of a boiler from an installer has a contract with that installer. The exact terms of that contract are dependent on the agreement between those parties.
Yep, a fully working system. The goods supplied must correspond with the description given, be of satisfactory quality; and be fit for the purposes.
If the manufacturer offers a warranty, then the purchaser also has a contract with the manufacturer.
Correct, I have never questioned or inferred that, that is not the case.
The purchaser, if not a business, also has statutory rights under specific consumer legislation, in addition to general rights under Contract Law.
That's right THE SUPPLY OF GOODS AND SERVICES ACT 1982
Now then, I expect you're going to insist that the consumer has no contract with the manufacturer. If you think this is the case, then please explain how any consumer has any rights under the terms of any manufacturer's warranty.
See above you poor mis-guided fool.
To illustrate your point, please name any consumer, any product, and any manufacturer you wish, and also the specific legislation that provides the non-contractual rights that you believe permits a consumer to claim against a manufacturer (e.g. The Ritual Humiliation Act 1971).
At this stage my "claim" would be against the supplier not the installer, did you not pick that up having read through this thread?
On the off chance that the boiler should prove to be defective and thereby pose a health and safety hazard I could rely further on the CONSUMER PROTECTION ACT 1987 in support of any potential claim.