On 10/11/2016 20:26, rick wrote:
On 10/11/2016 01:32, John Rumm wrote:

So back to question ... do I set the boiler to run the water at 75C,
then what do I set the pump speed at.. on old system you would adjust
pump speed to to get correct differential

If efficiency is your aim I'd ignore that and set to the lowest boiler
temperature that gives you sufficiently hot water and adequate space
heating, with your system as-is. (Min. 60 deg. for HW to kill Legionella
of course.)

Or would I be better setting at lower temp ... boiler has option to
limit flow temp to 63C by a control board jumper setting.

Yes, try it and see,

.... and pump is on max speed.

Temperature differential is generally not critical over quite a wide
range. I'd aim for the lowest speed that gives adequate performance.
Preferably keep the return temp down in the low 50s (or less) to keep
the boiler in condensing mode.

--
Andy