Aidan wrote in message
om...

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

snip

You would be very fortunate to find a UK 'heating engineer' who
understood such a system.

Also, the Americans generally have bigger houses, so it's more common
in the US. See ' Primary-Secondary Pumping made Easy' by Dan Holohan,
available from HeatingHelp.com. It's written for home owners, so it's
fairly free from techno-jargon. It's in US/Imperial units (gpm,
BTU/hr, degF) but it's easy to grasp.

If anyone else is reading this thread and wants some background information,
I came across Warmrite's "Manual Of Modern Hydronics" at
http://www.heatinghelp.com/pdfs/156.pdf

It gives loads of examples of different boiler/heating arrangements.