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Different Types of Boiler Explained

A gas boiler is essential in any home, providing heating and hot water on demand. However, picking the right gas boiler can be tricky, as there are many different types and sizes on the market. With so many options to choose from, it’s important to know what you need before making a purchase.

If you’re in the market for a new boiler, it’s important to understand the different types available and how to choose the right one for your needs. Here we’ll take a look at three common types of boilers – combi, system and Conventional (also known as heat-only) – and discuss the pros and cons of each. By understanding the different options available, you can be sure to select the best boiler for your home.

3 Most Common Boilers Types

There are three main types of boiler you will encounter when looking to switch or upgrade your home’s heating system:

1. Combi Boilers

A combi boiler is a ‘combination’ or all-in-one type of boiler. This means that it provides both heating and hot water on demand, without the need for a separate water tank or cylinder. Combi boilers are generally considered the most efficient type of boiler as they only heat the water that you need, when you need it.

2. Conventional Boilers

A conventional boiler (also known as a regular or heat only boiler) is the second-most common type of boiler found in UK homes. Unlike combis and system boilers, a regular boiler will require a separate hot water tank or cylinder as well as a cold water cistern (found in the loft). Regular boilers are slightly less efficient than combis and system boilers but are generally more reliable.

3. System Boilers

A system boiler is similar to a combi in that it also doesn’t require a separate cold water tank or cylinder. However, unlike a combi, a system boiler will have a hot water storage cylinder, which means it can store more hot water than a combi and provide it on demand. System boilers are generally considered less efficient than combis as they still need to heat water even when you don’t need it.

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So, which boiler is right for you? The answer will depend on your individual needs and requirements. If you need a new boiler, be sure to consult with a Gas Safe registered engineer who can advise you on the best type of boiler for your home!

Now that you understand the different types of boiler, let’s take a deeper look into how they work, their key features and the pros and cons of each of the boiler systems.

1. Combi boiler

Combi boiler

By now, you should have a good understanding of what a combi boiler is and how it differs from other condensing boilers, but before you’ll know for sure if it’s the right fit for you it will be useful to have knowledge of how combi boilers work.

How does a combi boiler work?

A combi boiler works by taking water from the mains supply and heating it instantly, on demand, as and when you need it. This means that there is no need for a hot water cylinder or cold water storage tank, which can save valuable space in your home.

A combi boiler, in most cases, is also a condensing boiler, which is more efficient than older boilers as it extracts more heat from the burning gas, reducing wastage as well as heating bills.

Another advantage of a combi boiler is that it can be installed quickly and easily as there is no need for extra pipework. This also reduces the risk of leaks as there are fewer joints and fittings.

What are the pros and cons of a combi boiler?

Pros of Combi Boiler

The pros of a combination boiler unit include:

  • Hot water on demand –

You’ll never have to wait for hot water as a combi gives you instant hot water and heat.

  • Compact design –

They take up less space in your home as there is no need for a hot water cylinder or cold water tank.

  • Reduced risk of leaks –

As there are fewer joints and fittings, there is a reduced risk of leaks in your central heating system.

  • Quick and easy to install –

With combi boilers, there’s no need for extra pipework, which also reduces installation costs.

Cons of Combi Boiler

The cons of a combi boiler include:

  • Limited hot water flow rate –

As these boilers heat water on demand, the hot water flow rate is limited and may not be sufficient for multiple showers or baths running at the same time.

  • Not suitable for larger homes or multiple bathrooms –

if you have a large home or family, you may require a higher hot water output which a combi may not be able to provide.

  • No backup when your boiler breaks–

As the combi boilers provide hot water and heating directly, there is no failsafe or back up when things take a turn for the worse. Unlike conventional boilers which often incorporate an electrical immersion heater system too.


Combi boilers are the perfect choice for smaller households and anyone looking for a compact, yet extremely energy-efficient boiler for their home where water pressure rates are adequate.

2. Conventional Boilers

Conventional Boilers

For a long time, conventional boilers were the standard set up for homes. As you’ve already learnt, they have three core components: a hot water storage tank, a cold water cistern and the boiler itself.

How does a conventional boiler work?

A conventional boiler system will have a boiler that is gravity-fed by a cold water cistern (usually in the loft) and store hot water in a separate hot water tank. These boilers are also known as ‘regular’, ‘traditional’ or “heat only” boilers.

Regular boilers function by supplying hot water straight to the heating system, for example the radiators, and storing hot water in a cylinder for when it is needed. As the water in the tank needs to be heated before it can be used, this means there can be a delay in access to hot water or heating if you do not have your boiler set to run at regular intervals. The plus side is that you will have a limited reserve of hot water at any one time.

What are the pros and cons of a conventional boiler?

Pros of Conventional Boiler

The pros of a conventional boiler unit are:

  • Better suited to larger properties –

A heat-only boiler can provide a greater flow rate and as a result, are more suitable for larger properties with greater hot water demands e.g. those with multiple bathrooms. 

  • More forgiving on water pressure –

If you have low water pressure in your area, a conventional boiler is more likely to still function as the water is stored in a cylinder.

  • Can utilise an electrical immersion heater –

An immersion system uses electricity to heat the hot tank should the boiler fail. One of those things that you may not use that often, but will be worth its weight in gold when you find yourself in the position of needing to.

Cons of Conventional Boiler

The cons of a conventional boiler include:

  • Heating water can take time –

As the water is stored in a tank, it can take time to heat up meaning you may have to wait for hot water.

  • Takes up more space –

A conventional boiler system takes up more space as it requires a cold water cistern and hot water tank.

  • Risk of leaks and burst pipes –

As there are more fittings and components, there is an increased risk of leaks or burst pipes with a conventional boiler. If not well insulated, the cold water tank can also freeze in the winter.


A conventional boiler is a good option if you have a large home as they can supply hot water to multiple bathrooms at the same time. They are also easy to service and maintain and can take advantage of an immersion system. However, they do take up more space than other boiler types and you may have to wait for hot water.

3. System Boilers

System Boilers

System boilers work in a similar way to a regular boiler, but with one important difference – the hot water is stored in a cylinder. Other than that, they work in the same way as a regular boiler when hot water is then channelled through your heating system.

How does a system boiler work?

A system boiler heats water directly from the mains cold water supply, as opposed to a regular boiler which heats water from a cold water cistern in the loft. The hot water is then stored in an unvented hot water cylinder, ready for when you need it.

This means that there is no need for a cold water tank, saving you a big portion of space. It also means that system boilers can heat up water much quicker than regular boilers, as there is no need to wait for the water to be heated from the loft.

What are the pros and cons of a system boiler?

Pros of System Boiler

The pros of this type of boiler are:

  • Quicker heating –

As the water is heated directly from the mains, it means that system boilers can heat up water much quicker than regular boilers.

  • Less space needed –

As there is no need for a cold water cistern or hot water tank, system boilers take up less space than regular boilers. This can be a big advantage if you have a small home or limited space.

  • Great for households with high hot water demands –

The large tank means they are ideal for big families or even shared accommodation as there is always a vast amount of water available.

Cons of System Boiler

The cons are:

  • Not a good upgrade from a combi –

If you currently have a combi and want to change it to a system set up, you’ll need to make sure you have ample space for the hot water tank.

  • Will also be affected by mains water pressure –

As this boiler type is also mains-fed, if your area suffers from poor water pressure then this will likely affect its performance.

  • May not be the best fit for older systems –

If you have older pipework or heating systems in your home then they may not be able to cope with the high-pressure output of this boiler.


Sitting somewhere between the combination variety and the regular setup, the system boiler will be ideal if you have a larger household that can make use of the hot water tank and your property has a water supply with sufficient pressure. You’ll reduce heating time and save space by not having a cold water tank but, if you’re changing from something else, you’ll need to make sure your current system can handle the higher pressure.

A quick note on condensing boilers

Condensing technology has been a mandatory requirement in all types of boiler since 2005. Condensing boilers make efficient use of every bit of heat that is expelled into the boiler reducing wasted gas, heavy emissions, loss of heat and — most importantly — heating bills!

All types of boilers installed by Aquatek

We’re Aquatek, and we’re a team of reputable plumbing experts who have been operating in Essex since 1988. We’re industry-leading when it comes to plumbing services, and we are dedicated to providing excellent customer service; so much so that we offer a 12-month guarantee on all of our work – including boiler repairs, installation, combination boilers, gas engineering, boiler breakdowns and central heating.

If you’re looking to get a new installation, change your current one or ask some further questions about the different types of boiler feel free to get in touch with a member of our team.

We can further advise you on what is the best choice for your requirements and even arrange a home visit.

Reach out to our team today.

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