System boilers have a pressure gauge on the front of the boiler, or beneath it attached
to one of the valves.This type of boiler heats a hot water cylinder, normally located in an airing cupboard.
Combi boilers have 5 (or more) pipes coming out of the bottom of the boiler. Th
ey heat water directly from the mains when you turn on a tap, so they do not need a tank or cylinder.
These are also called Regular, Traditional, Conventional, or heat-only boilers.
Standard boilers are fed by a tank (usually in the loft) and store hot water for later use in an insulated tank.