What different boiler types are there?

There are essentially 3 different boiler types:
Combi Boilers
Combi (or combination) boilers have everything needed to heat your radiators and deliver hot water to your taps. The boiler is a compact unit which means it is easy to fit in any home as there is no need for a hot water cylinder or water tanks in the loft.
Heat Only Boilers
A heat only boiler works works with a small expansion tank and a larger cold water storage cistern usually located in your loft space. Heat only boilers are also a good solution if your home has low water pressure or you have several bathrooms.
System Boilers
A system boiler is made up of a pump and expansion vessel and a sealed hot water cylinder. This provides hot water for the taps and heats the radiators. This is a space saving system as there is no need for a feed or expansion cistern in the loft.