I would have to say to you that doing nothing because of trying to
upgrade to a perfect installation is unwise. There are real and
substantial saving to be made with a modern boiler and controls.

Most of the boiler improvement comes not from the condensing itself
but
form a better heat exchanger in which condensing can and does happen.
The condensing is a bonus and increasing the emitters to reduce the
return temp is a further bonus.

Thanks. Understood and fully accepted. (A fuller account would have
gone on to say that I would expect to be able to get around 80% which
will be worth doing now we do not get the benefit of trogging off to
heated offices - but only after we have sorted out the roof, which comes
after sorting out the subsidence recently discovered..... )

In passing, I have now also read the printed report in Which? and still
think they are naughty not to explain what is required to get to 90%
efficiency.

--
Robin