Balancing CH and HW and condensing boiler questions

[Agile]

The pump speed should be adjusted to produce the desired temperature drop between the boiler flow and return pipes. Lower speeds mean a bigger temperature drop as more heat is lost before the water gets back to the boiler. This temperature drop will be larger than the temperature drop across any single radiator, sometimes a lot higher.

You do seem to have some very odd ideas about heating systems.

Unless the boiler is at the bottom of the garden and loses a lot of heat in the connecting pipes then the boiler return cannot be at a lower temperature than the average radiator return temperature.

To make it simple for you, imagine all the rads are turned off except just one!

In that case the boiler flow and return temperatures will be exactly the same as the radiator flow and return temperatures.

Tony