OTOH, this may have defeated some internal algorithms.

So it will modulate on the load compensation software, either in CHG
or DHW mode?

That I don't know. I suspect it will modulate on any mode. However, it seems
to be cycling on a regular basis anyway. Even modulated right down, my
average heating requirement is very low. It is an Edwardian terrace. I
calculated 8.4kW when it is -3C. At 10C outside, my requirement will be a
fraction of this (probably around 3-4kW) which is below the modulating
range. It definitely is modulating down, though, as the gas rate at the
meter varies.

At some point, I might bother to redo the heating circuit with a TMV and
pump to make the radiators cooler and reduce the return temp.

The pluming I get from it is very slight whatever the return temperature,
especially compared with the Icos I had in the last place, which created
sufficient fog bank to have saved the Tirpitz.

Christian.