Boiler info: combi, heat only and system boilers

Info: from Which feature writer Sam Morris 2021

Which is a really useful magazine: I wanted to write about boilersTypes of boiler

Combi, heat-only and system boilers.

A combination (combi) boiler is the most common type of boiler the UK.

Heat-only and system boilers suit a variety of situations

A condensing boiler could save you hundreds on your heating bills. 

50% of people surveyed by Which in 2021 say they look carefully at what’s available when they decide to change their boiler.

Combination boilers connect directly to the mains cold water supply and provide hot water on demand. A combination boiler doesn’t need a water tank and its components are housed within the boiler casing. The rate at which water is supplied reduces when the boiler is trying to provide hot water to two or more places at the same time and their effectiveness can be limited by mains pressure. The boiler unit contains moving parts. 

Heat-only boilers provide heat directly to your radiators and connect to a water tank to provide hot water. Using an on/off switch you can heat water in the storage tank and switch off when it’s not needed. It usually requires a cold water feed and an expansion tank in the loft. Components such as the circulation pump are housed externally. Water isn’t automatically heated. Heat is lost from the stored hot water in the cylinder.

System boilers known as ‘closed vent’ or ‘sealed system’ boilers, they require a hot water cylinder but not a cold water tank and components like pumps and valves are built into the body of a system boiler. It needs a hot water cylinder and the hot water tank needs to refill. 

Storage combination boilers work like a combination boiler with an internal hot water cylinder built into the boiler. With the hot water cylinder the pressure doesn’t drop when water is used throughout the house. Water can be kept warm with the addition of a solar thermal panel.

Storage combination hot water tanks are typically sized between 40 and 200 litres, but some hot water tanks for system boilers can be 500 litres or more. 

Condensing boiler

Condensing boilers are more efficient they produce fewer carbon emissions and can reduce energy consumption. A condensing boiler could save the average user between £45 and £300 a year on your heating bill (Energy Saving Trust, 2021). all boilers installed since 2007 are condensing boilers. A condensing boiler captures some of the heat from gas produced and uses it to heat water returning from the central heating system. As it requires less heat from the burner it is more efficient.


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