DOMESTIC RT LOOP PUMP

Louie O.

Gentlemen,
When a domestic hot water system utilizers a return loop pump where should the aqua stat that controls it be located?(inlet or outlet of pump)May I also ask the setting of stat to start and stop pump?
I always find them at the pump location, is this correct?

The next part is if the aqua stats location is at the pump and the stat turns off the pump, what is to prevent the loop in areas of the building from getting cold before the stat at pump calls again, especially if its in a warm location?
Thanks