In article , TMC
writes

I do not see how a booster pump can work with fixed volume output from the
boiler

Yep, that's right, flow will be limited by the heat output of the
boiler.

Worth noting too that you're not allowed to pump from the mains (either
on the cold feed or via the combi), only from a tank fed system. It's to
do with the risk of causing negative pressure in the mains and sucking
in impurities or bacteria.
--
fred
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