Gas boilers use natural gas or liquefied petroleum gas (LPG) as their source of fuel. Like most boilers, a gas boiler burns fuel to heat water.
There are different high efficiency gas boilers on the market and this selection gives the consumer the scope to purchase and fit the right kind of boiler in their property whatever their needs or preferences may be. There are many factors that can affect these needs and preferences from the amount of spare space in the property to a need for a continuous supply of hot water.
Vaillant produce three different types of gas boiler: combination (combi), system and open vented boilers. Each of the three types of boiler that are produced by Vaillant are high efficiency condensing boilers which, since 2005, have to be installed by law when a new boiler is being fitted in the United Kingdom.
Combination gas boilers make the use of a hot water cylinder redundant as they distribute hot water to a property on demand direct from a mains supply. By not needing to use a cylinder, a combination boiler frees up valuable space in the building. Combination boilers are so called because they heat water for both a central heating system and for taps/showers etc.
System gas boilers (sometimes referred to as sealed system boilers) do not require a cold water expansion tank so again can save space. This type of boiler has a hot water storage cylinder and is ideal for properties that have more than one bathroom or other multiple outlets where hot water may be required at the same time in different places.
Open vent boilers are usually connected to two tanks installed in a properties loft space. One of these feeds the boiler and the radiators and the other feeds an open vent hot water cylinder. As with a system gas boiler, this option is better suited to a property where several people may be using hot water at the same time as it can quickly supply multiple outlets simultaneously.