Most modern boilers are more efficient due to their condensing technology. Older boilers lose heat through exhaust flues; condensing boilers recover this to heat central heating water.
The two main types of gas boilers are :
Combi boilers– heat hot water on demand and don’t require a hot water cylinder or a cold-water tank, so you’ll save on space as well as your energy use. As a result, they’re often the best choice for smaller properties.
System boilers– have a separate hot water cylinder to store hot water. They’re usually best for homes with multiple bathrooms as they can simultaneously provide hot water to taps.
Your choice may also be determined by a need to work with renewable heating technology – system boilers are more compatible with solar thermal water heating and heat pumps.