"fred" wrote in message ...
In article , Dale Shuttleworth

3) If I go for a simple boiler like the Keston Celsius then I suspect
that the two requirements above may be somewhat incompatible. What
boilers are there that will provide different flow temperatures
depending on the source of demand? I'm aware of the MAN Micromat but
at the moment it looks expensive (1600 UKP vs a lot less than that
for the Keston with sealed system kit, even if I take into account
the fact that the Micromat integrates some of the controls - the
difference pays for a lot of gas!).

It was these two boilers I shortlisted for my installation. IMO the MAN ,
with it's proportional control, DHW setting and very low minimum
modulation, walks all over the Keston for this kind of job, but in the end
I
just couldn't justify the extra cost. The lack of a separate DHW demand on
the Keston is a major flaw, but I plumped for it knowing that I would be
attempting a bodge to correct the problem. The solution relies on pulling
the output of the boiler stat control when DHW demand is on.

"pulling the output"? What do you mean?

This is a
straightforward job as the control panel board is separate from the main
electronics and can be achieved with a mod to the loom comprising a relay
and a few resistors. If discovered, it would of course in validate your
warranty so is not for everyone. I will publish the mod here when it is
fully
tested.

Are you forcing the boiler to full unmodulated power when DHW calls? BTW,
the Ravenheat CSI system boiler has this function. Why any load
compensation modulating boiler does not have this simple function is beyond
me. It can be selectable, by moving jumpers, if need be.




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