YAPH wrote:

So in practice I'd say set the boiler temperature control about halfway to
start with and experiment. If it doesn't get the house up to temperature
in very cold weather turn it up until it does. Not ideal in this age of
programmable, automatic controls, I know.


There is another issue here, which is the central heating pump.

A higher water temperature will mean that the pump runs for less time
each day. Lowering the water temperature to the point where the pump
runs almost all the time might be more energy efficient at the boiler,
but it definitely uses more energy to run the pump for longer.

How the additional energy used running the pump almost all the time
compares with the energy saved by using a lower water temperature, I
don't know.

Apart from the additional energy, there is also the question of the
reduced pump life resulting from extended running.