"Christian McArdle" wrote in message
...
If that is the case, what will be the flow temp. Assuming that the
boiler will lift the temp say 20 degrees. If the return temp is say 45
then the flow temp will be 65. Going through a heat bank previously
heated to say 75, then it will have a cooling effect on the heatbank.

Nope. If you take water out at 25C and return it at 45C, then it will heat
the heatbank, even if most of it was previously at 75C and the hot water
is
deposited at the top.

Is there not a boiler out there that could supply heating to the
heatbank at say 75 degrees until it is totally satisfied then
reduce its temp down to say 65, to ensure that the return is
well within the condensing range.

Worcester Bosch Greenstar System with the optional diverter valve allows
separate setting of water and CH temperatures. You can further subzone the
heating side with S-Plan if you have multiple zones. I have the boiler
without the diverter and was only aware of it from reading the
instructions.
I seriously wish I had bought the option, as it would have enabled me to
run
the heating at a much lower temp.

The W-Bosch setup. Do they extra controls for DHW and CH and it diverts to
suit? I can't remember now.

IIRC, the W-B maintains a constant flow temp and modulates to maintain that.
You can install your own diverter valve and fit a weather compensator. It
will switch in and out the boiler to maintain the compensator setpoint,
which will be low most of the time. Compensators have anti-cycle control on
them.