Megaflo

[tom squires]

Advantages
There are a number of advantages with using an unvented hot water cylinder. For example:
High water pressure - great for showers so no need for booster pumps

Balanced water pressure at hot and cold taps/faucets

Balanced shower pressure - allowing for safer temperature control

Better high pressure terminal fittings - such as taps/faucets and valves

No cold water storage cistern/tank - enabling loft conversion

Improved cylinder location flexibility due to mains water pressure

Quicker to install than an open vented cylinder and its associated fittings

Disadvantages
The disadvantages with unvented cylinders are:
With low mains water pressure and poor flow rate, the system may be unable to operate

No water storage in the event of a water mains failure

Extra controls occupy more space (unless using a composite/combination valve)

Price - unvented cylinders usually cost more than open vented cylinders

[oilman]

also MUST be registered with Building control if installed badly they are very dangerous