There are different types of boiler: 

 

COMBINATION (OR COMBI) BOILERS - heat water instantaneously on opening a hot tap, so there is no need for a storage cylinder. 

 

SYSTEM BOILERS - these are designed to generate heat for your home as well as hot water that can be stored in a separate hot water storage cylinder. This can be situated anywhere in your home with no need for a separate tank in the loft. 

 

HEAT ONLY BOILERS - work in conjunction with a hot water storage cylinder and cold water top up tanks to provide both central heating and hot water. 

 

The type of boiler you need will depend on a number of factors, such as the size of your house and your hot water requirements.