"Aidan" wrote in message
oups.com...

Mr Fizzion wrote:
Can you have such a thing or is this one of Doctor Evil's fantasies?

Assuming youre referring to a secondary circulation loop on the hot
water supply system, then;

The combi fires on a draw off from the hot water outlets. The only way
I could imagine installing a circulation loop would be to install a
heat exchanger (tube-in-shell, preferably) on the secondary return

Boy are you confused.