How does a gas boiler heat water?

daymobrew

I am trying to understand how a boiler heats my hot water.
I understand the immersion as it simply heats the water already in the tank, just like a kettle.

For a boiler it heats water and this goes into the tank. If there is water already there, is it somehow pushed out?

I assumed that the my hot water tank is replenished with cold water as hot water is used so there is no obvious space for incoming hot water.

The hot water tank is an insulated tank in the hot press.

secman

The hot water from the heating system runs through a coil of piping within your cylinder in the hot press. So it is in fact like your kettle ,. As you draw hot water from cylinder , it is replaced by cold water .

Egass13

Google images of indirect cylinder, it'll show you diagrams of how it all works

Egass13

Google images of indirect cylinder, it'll show you diagrams of how it all works

daymobrew

Here is an image which explains it to me: http://www.ultimatehandyman.co.uk/cylinder.gif