That assumes that the boiler is a simple on/off type which is the
assumption of the whole document and those referenced by it.

I don't get that assumption at all. Why do you think that turning off the
boiler when no heating appliance requires heat is specific to an on/off type
boiler? It is simple to do, cheap and effective to turn off the burner when
no heat is required, whether it is a modulating type or not. OK, an old open
flue boiler suffers more from short cycling than a modulating condensing
fanned flue boiler, but the primary circuit losses are the same for both.

Obviously, with analogue TRVs and a modulating boiler you have the advantage
that the system can modulate down and bumb along nicely. However, there are
still savings to be made when the system really doesn't require heat, and by
a very simple, cheap and effective system, too. The cost of a flow switch is
very small, and it is wired up in the same way as a room stat, just
requiring to be inserted into the correct bit of pipe. (i.e. after the
bypass). The pulsing pump system is optional (but could save quite a lot of
cash, if you run an 80W pump 24/7).

Christian.