Choosing a combi boiler for domestic purposes can be tricky since many different aspects are to be taken into account. First of all the cost. Then how big the house is, required hot water per day among other things.
According to the new laws now, central heating boilers should be high efficiency condensing boilers unless ofcourse it becomes too expensive and impractical to install one.

For the purpose of attaining high efficiency,a combi boiler has been developed. A condensing boiler is a boiler which provides heat for central heating and thus hot water is got instantly at the opening of the tap. These centrally heating boilers do not require any copper storage tanks for storage of the hot water and thus a lot of space and cost is saved here.
The main advantage of the combi boiler is that the installation cost is very less and the maintenance cost is even better.