They do a fixed price repair for £311. This covers most parts, excluding the expensive bits like the big circular heat exchanger and the expansion vessel. (Why not the expansion vessel? It's not that expensive, surely?)
Or for £312 they do 6 months cover from Domestic & General. This covers any repairs needed during the 6 months, up to £1500 total, including the initial repair.
It seems a no-brainer to go for the D&G option, then cancel after the 6 months. What am I missing?