This gets a little more complicated. You basically need the pump overrun
output of the boiler to run the hot water pump.

So where does the heat go if the taps are turned off?

Didn't you mean the central heating pump ?

No, the pump for the hot water primary circuit is more suitable for pump
overrun than the central heating circuit. Don't get confused with the DHW
secondary, which is isolated from the primary system.

Christian.