Unvented cylinders are covered by Building Regulation Part G, where stored water capacity exceeds 15 litres. and provide hot water at mains pressure to your hot water taps. Plumb Thermals are qualified under G3 to install, modify or service your unvented hot water cylinder.

Unvented cylinders main advantage is the provision of mains pressure hot water throughout the house without the cost of booster pumps nor the requirement for a cold water tank to be sited above the highest hot water outlet, eg an upstairs shower head. By bringing the cold supply from the combination valve you can also ensure a balanced pressure in the hot and cold supply throughout the house. 

The disadvantage is the lack of hot water provided if there is an interruption in mains water supply. 

Indirect hot water cylinders are heated by your boiler, and normally have an immersion heater as a back up.

Direct hot water cylinders are only heated by the immersion heater.

Buffer cylinders, also called actuators or stores, are used to take up excess heat from a heat source, hold it in a store, to be able to distribute it through the heating system as soon as it is required. It stops the need for the heat source to be continually starting and stopping, thereby making it more efficient and lengthening its lifespan.