Here are the main types of gas boilers:
Combination Boiler Systems
Combination boilers are great space-saving solution because there is only need for one appliance. This is why they are commonly used in London in small houses and flats.
With a combination boiler, there is no need for installing a separate hot water cylinder or a water tanks in the loft. The boiler heats hot water instantaneously giving you sufficient pressure to your hot water taps as well as doing its normal job of heating your home.
Unvented Hot Water Systems
Unvented hot water systems require 2 appliances and some additional controls. It requires both a boiler and an unvented hot water tank (normally located in the airing cupboard.
This system will give you advantage of running two (2) hot water taps at the same time without reducing the hot water pressure. It is great for bigger family homes and or homes with two (2) or more bathrooms. Ideal for homes with low water pressure.
Conventional Boiler System
Conventional systems require 3 appliances which include a boiler, hot water cylinder and tanks in the loft. Slowly being eclipsed by the other types, these are the “header in the loft” type boilers.
The entire system is fed by two open header tanks in the loft. For central heating, a pump outside the boiler is used to pump water to the radiators. The domestic hot water, meanwhile, is stored in a cylinder tank. This system have drawbacks which include low water pressure at the taps nearest to the loft tank.