Why? is there a reason, you want/need to know? Do you want to know what people think is the best/cheapest?
The most common (that I've come across) for a free standing/ Back boiler/ system boiler. For an average size 2/3 bed house is the Grundfos Selectric 15/50.
Baxi/Potterton combi's 28/105 + use the Grundfos 15/60, Smaller boilers use the 15/50.
15/50 - 5 metre head 15/60 - 6 metre head
There's also Wilo pumps that are quite common, but there's many manufacturers out there.
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