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Hot Water Systems

Vented and Unvented Systems Maintenance

Both System and Regular boilers rely on cylinders to store hot water, but the type of cylinder you use — vented or unvented — is up to you.
The main difference between them is the way each cylinder is supplied with water.
An unvented hot water cylinder takes its water supply directly from the mains.
Whereas a vented cylinder is connected to a water tank (by a vent pipe, hence the name.)
This water tank is stored in the loft as it relies on gravity to pull the water down into the cylinder and through the pipes of the house

Vented Cylinders
In a vented cylinder, water from the mains is kept in a tank in the loft. The natural pull of gravity carries this water, via a vent pipe, down to the hot water cylinder which is usually stashed away in an airing cupboard.


Unvented Cylinders
In an unvented cylinder there is no need for a cold water tank in the loft. The cylinder is connected directly to the mains and the pressure of your water should be stronger.
The water is then heated within the cylinder but, unlike vented cylinders, there isn’t a vent pipe or tank to cope with excess water as it heats and expands. To remedy this unvented cylinders have inbuilt safety features like an expansion unit at the top or an air bubble that is inserted at installation.


Expansion vessel
This is used to deal with the expansion of the water in the system as it is heated. As water gets warmer it gets bigger, by up to 4% in volume. The water has to go somewhere, the expansion vessel is designed to store this extra water and stop the parts of the system bursting.