"John Aston" wrote in message
...

"Aidan" wrote in message
om...

It (primary/secondary pumping) is very rare on UK domestic
installations, mainly because of the costs.

Interestingly, having spoken to their technical departments, both Viessman
and MHS *require* the installation of low loss headers if any pumps are
installed in the heating system (other than the boiler's pump, of course)
running off their modulated boilers.

MHS supply a Strata 1 boiler. It is a re-badged version of the Eco Hometec
Micromat EC. The Eco Hometec literature shows a Y-plan zone valve
installation with a supplementary pump in the radiator circuit. The MHS
literature shows almost the same arrangement as an example of an incorrect
installation!

(For flow control, Viessman Vitodens can be connected to a sensor that
monitors the header temperature. The Strata 1 just monitors the
temperature
within the boiler.)

I think that I've got enough information to come up with a draft heating
system design. I'll probably post it on the web and invite comments. This
newsgroup has been an excellent source of help in that respect.

With condensing boilers headers reduce efficiency. With a condenser you
don't want very hot water feeding right back into the return. This raises
the return temp which reduces efficiency. You want the return temp as low as
possible. Best use a heat bank or thermal store, which is a great neutral
point, and have the boiler heat that directly. For most of the re-heat the
return temp will be low.

All headers are neutral points for circuiots to tee into. A heat bank gives
you that and a DHW store with instant high pressure DHW. You only need cheap
simple boilers with a heat bank, one of its selling points.

I'll try and come up with some alternative systems.