Luckily there are only two main types: "Sealed" and "open vented".

Sealed systems can be identified by a pressure gauge on the boiler, while open vented systems have a feed and expansion water tank in the loft, there normally is 2 whater tanks in the loft a large one and a small one, this is the small one. On open vented systems you should also have a cylinder (white or orange) for the hot water, somewhere else in the property, normally in an airing cupboard.