A CH pump in the cool bottom section of the cylinder. It will remain cool with a more even temperature over the pump. Heat from the pump is captured. Immersed pumps are common. There is no reason why they cannot be immersed in heating and water systems.
Here you go, you said about a CH pump immeresed in the bottom of the cylinder, I am just asking for you to give me details of a CH pump that does this, as far as I am aware they do not exist