The company came out and said it was a maunfactures fault at glow worm
and they will deal with it. Someone must be responsible for the
failure of the boiler and the ensuing damage.

The whole thing sounds like a legal quagmire. After all, you don't actually
have a contract with the manufacturer, apart from their voluntary guarantee
which can exclude what it likes (and almost certainly excludes consequential
damage).

That leaves the original installer (who are responsible for supply goods
free of manufacturing defects) and the servicing company as well. Given that
you only guarantee is that they will disagree over the cause, it would be
seriously complicated to even know who to sue, let alone put together a
watertight case.

Personally, I would forget about the entire thing and hope my insurance
covers it.

Christian.