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from NT contains these words:

As I said you don't seem to know what latent heat is.

I dont think theres any basis for that claim at all. I've said further
back in the thread that the latent heat of vapourisation _is_ the plus
point of condensing boilers.

But you had it in the heat exchanger when the boiler was not firing.

What you are
referring to could be called residual heat but no way would anyone with
any real understanding of the situation would call it latent heat. It is
not even a proper use of the word 'latent' even if the associated 'heat'
is ignored.

according to dictionaries it is an appropriate use of the word.
Perhaps you know better than them?

I know how to consult a dictionary. You have just proved you don't.

From the Concise Oxford:

"latent /.../ adj.
1 concealed, dormant.
2 existing but not developed or manifest."

There is nothing remotely concealed about the heat in the heat
exchanger. Perhaps you had in mind Collins Dictionary's 4th meaning:

"(Psychoanal.) relating to that part of a dream expressive of repressed
desires."

But I wouldn't care to speculate what particular repressed desire is
hidden in your heat exchanger.

In contrast latent heat (Oxford again):

"latent heat n. Physics
the heat required to convert a solid into a liquid or vapour, or a
liquid into a vapour, without change of temperature."


And just to throw another spanner in your unworkable hypothesis when the
boiler isn't firing the the heat exchanger becomes a radiator and one of
the characteristics of a radiator is that it radiates. It probably
radiates marginally more heat than it loses by conduction. Signification
radiation won't escape out the flue.

Obviously there will be some radiation, conduction and convection. I
dont think thats news.

And the radiated heat escapes out of the flue precisely how?

--
Roger Chapman