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.