I think you are slightly missing the point!
The manufacturer may give a guarantee ( actually a warrantee! ) at his discretion and subject to whatever terms they may impose.
However, the boiler maker has to comply with the Sale of Goods Act which requires that the boilers are of "merchantable quality". Most construe that to mean they have to put right any that fail within a year. Thats regardless of who has fitted them as long as they are fitted safely.
Tony
The manufacturer may give a guarantee ( actually a warrantee! ) at his discretion and subject to whatever terms they may impose.
However, the boiler maker has to comply with the Sale of Goods Act which requires that the boilers are of "merchantable quality". Most construe that to mean they have to put right any that fail within a year. Thats regardless of who has fitted them as long as they are fitted safely.
Tony