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What is a combination (combi) Boiler?

Combi boilerA combi boiler is a heat source that can provide hot water and space heating. As there is a constant push to find more reliable and efficient ways to produce and conserve energy, combination (combi) boilers have become a great option for many homes in the UK.

There are four different types of fuel that combi boilers use, including:


Within the United Kingdom, most homes are connected to the gas network. So, Gas Combi boilers are the most common, and one of the most suitable type of boiler to ensure efficient and cost-effective to the majority of homes in the UK.


Oil combi boilers tend to have a highly efficiency return on each energy unit, around an impressive 92-95%. Alongside the oil combi boiler system, an oil tanker will have to be installed outside of your home and topped up by an oil supplier to keep the system running. Usually, this serves as no issue space wise, and is a popular choice if your home is not connected to the gas network.


Liquified Petroleum Gas combi boilers are made up of 66% gaseous hydrocarbons extracted from natural gas and oils, and the remaining 34% from oil refining. LPG combi boilers systems require an additional fuel tank, similar to that of oil combi boilers, outside of your home that will require a supplier to replenish the fuel supply when It runs out.


Electric combi boilers systems include the same standard wet central heating system to heat up water. However, unlike Gas, oil and LPG combi boilers, they use electricity to heat water rather than using energy from burning fuel. Electricity is stored during off-peak electricity periods which is then converted into heat that can be radiated throughout your home the next day. Therefore, electric combi boilers are limited in their abilities to produce hot water readily and are usually not suitable for larger homes. For a small home, it may be an option where oil and LPG is too expensive or the installation of the oil tanker outside of the home is impractical or unsuitable for the home space, or the home is not connected to the gas network for a gas combi boiler.

Now-a-days, the majority of contemporary combi boilers have a condensing mechanism incorporating a Flue Gas Heat Recovery System. New combi boilers use less energy by utilising the heat and gases that would otherwise be wasted, recirculating them to warm up new, cold water from the boiler as it moves to the mains.

Why would a Combi Boiler benefit you?

Arguably the greatest selling point of combi boilers is their high energy efficiency, subsequently lowering your energy bills. Legally, you are guaranteed at least 92% efficiency with the installation of a combi boiler. Although, combi boiler efficiency tends to average above this minimum, in comparison to older boilers which tend to produce only 55% efficiency. That’s 45% wasted energy!

Simplistically, installing a combi boiler means all your heating and hot water needs are all in one place. As a separate cylinder and water tank isn’t needed, like with a conventional boiler, you’ll have much more space where your cylinder would have been (e.g. in a cupboard) and where your water tank would have been (e.g. in your loft or attic). So, an all-in-one unit is not only compact, saving you space in your home, but it is also much easier to install.

However, as the whole process is centralised within one unit, there may be a slight reduction in water pressure if you try to use more than one hot water tap at the same time in your home. As soon as the other hot water taps are turned off, water pressure will solve itself almost immediately. We consider this a very insignificant, short-term effect when considering the benefits of combi boilers. Although, in general, you will get a much stronger hot water pressure as water is flowing in straight from the mains. If you’ve ever had to live with a conventional boiler, you’ll definitely understand the annoyance of running out of hot water and having to wait for it to reheat whilst you’re running your bath! With a combi-boiler, you’ll never have to worry about running out of hot water.