Minor point, but the immersion is the heating element that extends to within the tank, short for "immersion heater".
The tanks generally also have a heat exchanger within that's hooked up to the wet central heating system, that way you can have 1 boiler so both central heating and water heating.
The tanks generally also have a heat exchanger within that's hooked up to the wet central heating system, that way you can have 1 boiler so both central heating and water heating.