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Boiler Advice

What is a Combi Boiler and How Do They Work?

What is a Combi Boiler and How Do They Work?

If you have an old boiler and are considering a new one, then you may have come across different types of boilers or wonder what type of boiler you have. One of the most common boilers in the UK is the combi boiler.

You may wonder, “What is a combi boiler?” Combination boilers were initially meant to consolidate all components of a typical central heating system into a single compact device.

A combi boiler is a type of boiler that can supply both hot water as well as central heating on demand.

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How does a combi boiler work?

You may find yourself asking, how does a combination boiler work? A combi boiler works by using condensing technology to efficiently heat the system water via latent heat from flue gases. When you need heating and hot water, the combi boiler’s gas burner is activated.

how does a combi boiler work

The heat created by the flame is transported to the primary circuit via the main heat exchanger, where it is sent to either the radiators or your hot water taps through a plate heat exchanger.

Most modern combi boilers also include a pre-heat system, that enables the boiler to store a limited volume of water that may be used later.

The water is kept in the boiler all day and kept at the desired temperature so that it may be rapidly delivered to the hot tap.

What is condensing technology?

Condensing technology lowers the heat loss of fuel combustion, efficiently absorbs the heat energy provided by the fuel, and at the same time, dangerous toxins in the flue gas are gathered into the condensed water, reducing acidity and other pollutants.

Smokeless combustion technology is used in more sophisticated condensing gas boilers, which decreases nitrogen oxides.

What benefits does a combi boiler have?

What benefits does a combi boiler have?

A lot of homeowners prefer combi boilers because of their many advantages:

Compact size

The size of a combi boiler is one of its advantages. Combi boilers do not require extra storage tanks, therefore the entire system may be managed by a single appliance. Hot water and heating are included.


Efficiency is another benefit of a combi boiler.

A flue gas heat recovery system, which is integrated into certain contemporary combi boilers, uses the gas produced while burning gas or oil to heat water that is brought in from the mains. As a result, the system can burn less fuel and reach an efficiency of over 90%, resulting in lower heating costs for a home.

Keeps costs down

When opposed to installing a conventional system, which often calls for tanks, a hot water storage cylinder, pumps, etc. buying a single unit (a combination boiler ) can be less expensive than buying many system components.

Hot water on demand

Combi boilers are an excellent option for high hot water demand since they can heat water rapidly when necessary. Combi boilers warm water when needed, as opposed to a system boiler or conventional boiler, which heats and stores predetermined amounts of water in preparation. Therefore, a combi can deliver hot water continuously.

More affordable

When compared to a traditional heating system, the installation cost of a combi is lower. Combi components are also widely available. The entire combi boiler system is less complex, and installation takes only a few hours.

Disadvantages of Combi Boilers

Combi boilers are not appropriate for bigger households

A combi boiler’s capacity to provide water at any given moment is undermined by its compact size; as a result, normally only one faucet or outlet may be utilised successfully at a time on an ordinary combi boiler.

While a combi boiler may do just fine for many houses, larger homes with more bathrooms will need hot water at a rate that a combi boiler cannot keep up with. Due to its exterior hot water tank and alternatives for hot water pressure delivery, a system boiler may be better suitable in certain situations.

They need a strong main pressure

Another problem is that if numerous faucets and showers are opened simultaneously due to combi boilers drawing water straight from the mains, the water pressure will drop quickly.

Therefore, regular or system boilers that get their water from a hot water cylinder are sometimes better suitable for larger households.

How long do combi boilers last?

If you were wondering how long boilers last, they usually have a lifespan of 10-15 years, depending on the model and how frequently they are maintained. Regular boiler service may prolong the lifetime of a combi greatly

How much does it cost to install a combi boiler?

The cost of combi boiler installation varies according to the manufacturer, model, and size. Combi boilers may range in price, with bigger and more efficient ones frequently costing twice or even three times as much as cheaper variants. It is also necessary to consider the cost of installing the boiler.

Different sizes and types of boilers fit different requirements and property types, so it is always better to get guidance from a local expert to figure out the best solution for your home.

If you have a combi boiler installed, we have a selection of Which? Best Buy combi boilers.

These best comb boilers provide high performance while keeping energy efficient, they can also lower energy bills and heating bills. Speak with us to find your ideal solution and to take advantage of extended warranties.

What are the differences between both combi boilers and regular boilers?

Three types of boilers may be used to heat our houses. The combi, the system, and the regular boiler. All three serve unique roles and are best suited to various sorts of homes.

Regular boilers, sometimes known as ‘conventional’ boilers, are commonly found in older homes and are regarded as the least desirable of all boiler types, they most likely have become an old boiler, hence we recommend a new boiler. T

This is because a standard boiler can only heat your central heating and requires an extra hot water storage tank to provide you with hot water (thus the term ‘heat only’).

Furthermore, the entire system necessitates a big tank of cold water, often housed in the loft, to provide the boiler’s water supply, whereas other boilers acquire their water directly from the mains. As a result, the conventional boiler is the largest and most difficult-to-install type of boiler.

Regular and combi boilers differ primarily in two ways:

  • Room:

    A combi is designed to be very simple. It heats up and distributes water straight from the mains water supply. This means the combi may be quite small, saving space. The normal boiler, on the other hand, requires a lot of space due to its extensive pipes and many tanks.

  • Water usage:

    The second, and perhaps most essential, the distinction between the two boiler types is the amount of hot water they can produce. A combi is ideal for small to medium-sized houses, but if you have multiple bathrooms, the combi will be insufficient to heat and provide water to several taps at the same time. This is when a huge hot water storage tank comes in handy.

Combis are great for people who have limited space as well as a low to medium demand for hot water. If you have multiple bathrooms, you may want to consider another option. W

While a regular boiler can satisfy a high water demand, a large amount of space required and labour expenses to build this complex heating system mean that conventional boilers are no longer encouraged unless you are merely replacing an existing regular boiler.

Like the sound of a system boiler but don’t have the space? why not consider a storage combi boiler that combines the best of both boilers? Read our storage combi boiler guide for more information

What is a gas combi boiler?

Gas-powered combi boilers use natural gas, which is delivered to houses via the national gas grid network. Because most houses in the UK are linked to the grid, this is the most widely utilised boiler fuel because it is the simplest and quickest fueling choice.

Although natural gas is derived from fossil fuels, which are known to be harmful to the environment, it is still regarded as the cleanest and least expensive fossil fuel available, especially when compared to oil and coal.

What is an oil combi boiler?

Oil is considered a cost-effective option for residences that are not linked to the gas grid. However, if you have access to gas, it is not normally suggested because there are many more complications with oil.

Oil combi boilers tend to be much larger than gas combi boilers and are often kept outside due to them requiring large amounts of space to be put on. They are usually floor standing boilers too due to their size and weight.

Oil must be stored in an external tank, which must be kept on your land, as a fuel source. This might entail losing garden space or having to pay to have the enormous tank lowered into the earth. You should also plan and obtain refills to ensure that your supply does not run out, otherwise you may be left without hot water.

What is an LPG combi boiler?

LPG is an abbreviation for Liquefied Petroleum Gas, which is a byproduct of natural gas and oil extraction. It is a far less expensive and somewhat cleaner alternative to oil, and many more manufacturers are now offering LPG-compatible boilers. This provides you with additional options and is an excellent option for folks who do not have access to the gas grid.

Where can I get a new combi boiler?

If you want a new combi to save money and you’re looking for a highly energy efficient one, look no further. We sell modern boilers, so as technology advances so do our boilers. Don’t forget you can reduce energy waste with a smart room thermostat.

Short Summary about Combi Boilers:

  • A combi boiler is a boiler that can deliver hot water as well as central heating in the same system.
  • The benefits of a combi boiler are its compact size, high efficiency, and ability to effectively manage hot water on demand.
  • Combi boilers have a lifespan of 10-15 years.


Is a combi boiler electric or gas?

Combi boilers operate on either gas or electricity, depending on your needs.

What combi boiler problems are the most common?

Most combi boiler problems are identical to those seen with any other home heating system. For example, chilly radiators or a decline in boiler pressure. If you smell gas or suspect a gas problem, call the gas emergency services as soon as possible.

What combi boiler size do I require?

The size combi boiler you need depends on your heating requirements, each home will require a different boiler size (also known as boiler power). It is generally defined by the number of radiators. There are certain things to consider when purchasing a combi in terms of boiler size. One of the most crucial is that combi boilers are not ideal for houses with a high demand for hot water.

Is a combi boiler worth the investment?

If you live in a small house with low water demand, a combi boiler might be an excellent investment. Despite a few limitations, switching to a combi boiler may save you not just money on your costs but also a lot of effort.

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