tim... pretended :
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as

I have an opened vented system, with stored HW and the house is heated
by the one boiler, installed new last March. A Vailant ECOfit Pure 418.
We like the stored water to be good and hot, the boiler only has one
temperature setting available for its output temperature - so I have it
set at its max, of 75C, in order to meet our HW needs. The house
heating would be satisfied by a lower boiler temperature around 60C and
it would be more gas efficient, but unless I manually manage the
temperature setting I am stuck with the less efficient 75C.

I even tried to find a way to fool the boiler into working at a lower
output temperature, by adding a separate bi-metal stat on the boiler
output pipe to CH only, set at 60C, to shut it down at that temperature
- as heating satisfied. That was a miserable failure, in that the
boiler constantly cycled on/off via the stat, whilst ever the room stat
indicated a demand, rather than modulating its output down - as it
would on its own as it neared its 75C setting.

If anyone knows a workaround, to allow split boiler output temperatures
on this boiler - do let me know please.