What is a Combination or Combi Boiler
Combination boilers combine the functions of a central heating boiler and an instantaneous multi point water heater. They give priority, in the main, to the supply of domestic hot water (dhw).
The combination boiler has all its operating components contained within the casing and is typically designed for use within a sealed central heating system. A combination, or combi boiler, removes the need for separate water tanks as it’s cold water supply is taken directly from the mains water and it heats the hot water instantaneously removing the need to store hot water unless you really want to.
How Does a Combination Boiler Work
In really simple terms the fuel supply (usually gas, sometimes oil) comes into the boiler and is directed to the burners in the boiler.
These burners are activated by messages from the valves in both the central heating and hot water systems in your home. If a valve (tap) is turned on which asks for hot water to a bath for example, the open tap allows the water to flow.
The flowing water in the boiler runs over something called a paddle switch which turns the burners on in the specific part of the boiler which heats the water for the taps (The Domestic Hot Water System).
Any surplus heat is stored in a heat exchanger, a small compartment within the boiler, so when (for example) the central heating is in full flow, the surplus heat in the heat exchanger is used to heat the hot water for the taps or domestic hot water system.
Both the domestic hot water pipes and the central heating pipes run through the heat exchanger so one can always heat the other. This allows for both systems to be hot at the same time.
Condensing combi boilers are highly efficient and most are now manufactured with an efficiency rating of 90% or better. They use heat in the waste flue gas to pre-heat the cold water going into the boiler, hence this high level of efficiency.