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Last updated: 26th October, 2022


Central Heating Boilers

Central Heating Boilers

How do you decide which boiler is actually right for your central heating needs?

Central Heating Boiler Types

There are a few basic boiler types to consider when looking into central heating boilers since no single design is best at everything.

Whether you have an idea of the general category you are looking for or want to get an idea of the different boiler designs out there, it is a good idea to know what basic types you'll find.

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Combi Boilers

Combi boilers offer heating and hot water through one single shell in exchange for a lower overall water pressure. They can't produce a lot of hot water all at once, but combi boiler designs save on space thanks to the compact frame and are perfect for a smaller property.

These combination boilers combine two key product types into one compact design, which will free up plenty of space. This combination is weaker than each individual appliance or product, but a combi boiler installation is faster, and the free space is extremely convenient.

System Boilers

System boilers are like larger combi boilers, providing heating and hot water while also using a water storage tank to make sure that there is a reserve left if the mains supply goes down. They are often very large and powerful, using more fuel and taking up much more space compared to compact options.

A system boiler works best in larger properties. They are perfect for the delivery of water to multiple bathrooms and other appliances and can handle a high demand across multiple rooms.

Heat-Only Boilers

A heat-only boiler only offers central heating and no hot water for bathrooms or other uses, giving it much greater efficiency but at the cost of removing multiple other uses. These are best as a new boiler in a space that already has a hot water supply, providing much better conventional heating through radiators and other water-based heating appliances.

Boiler Features To Consider

Central heating boilers can come in a wide range of forms, and each boiler type can vary heavily within its own category. There are also countless attachments to install, alternate designs that include their own special features, and even some central heating boilers that are only meant for specific property types.

Condensing Boiler

Almost all boilers can have condensing features that allow them to recycle water vapour. As cold water heats up to a near boiling point, a lot of it will evaporate, and a condensing boiler turns this back into cold water while transferring the heat into the outgoing water as well.

This leads to much greater heating efficiency and a reduction in energy bills, which can be useful regardless of how much you are having to heat with your new boiler. However, they can also be harder to maintain than a conventional design and might demand more space (as well as better ventilation).

Water Pressure Controls

A regular boiler will generally have pressure controls, letting you change how much pressure the water is subjected to during the 'delivery' to the radiators or other appliances. This saves you from having to hire an engineer to rework the controls inside the boiler like a traditional design, but there are still limits to how high it can go.

The Storage Tank

Most boiler designs (except combi boilers) need a water storage tank, sometimes multiple. Everything but a combi boiler will usually have this.

A combi boiler does not generally have a tank other than the one inside the combi boiler itself. This makes it the exception – it is much easier to install but doesn't come with a tank as standard.

Ventilation and Flue Designs

The flue controls the delivery of waste gases to the outside of the boiler, which often means that you need ventilation nearby. Fossil fuel and gas boilers can also produce CO2, which needs to be vented out safely to keep your heating system safe. The flue helps manage this and might come with a filter or a non-traditional design that is easier to use with an existing vent.

Dimensions Of The Boiler

The size of your boiler impacts efficiency, space, and how quickly a hired installer can set it up. Size also changes how important a well-placed flue can be since a larger boiler means more gas coming up the flue. A bigger unit can require more room to install, so you can only place that unit in rooms that are large enough.

Hot Water Cylinder

The hot water cylinder is the heating element of most new boiler designs, but the design of this hot water cylinder changes how quickly it can heat up the water inside it. Direct designs can be faster but less efficient, while indirect ones are a better use of energy but take longer to heat up a given amount of water.

Vertical Movement

Boilers often need to deal with more than one floor. Boilers on the ground floor have to move water upwards, and boilers on a higher floor need to let it flow downwards. Gravity can handle downwards movement, but higher pressures and better flow rates can be vital for getting a boiler to heat bathrooms above it.

Boiler Filter

Most central heating systems use filters to clear debris out of the hot water. A heating system boiler can benefit from a good filter, but that is another piece that you might have to buy, with its own price and VAT to consider.

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Choosing Your New Boiler

Finding the best combi boiler for your situation is not just about looking at a number rating as you browse through reviews. No matter how many you browse per page and what kind of number sites are rating them at, most of the credit should go towards your own understanding of what you need.

Upgrade or Replacement?

Are you looking for a product that replaces your old boiler, or do you want boilers that are better than what you had? Improving your system boiler can make it more effective, but it might also consume more fuel or heat up slowly, two things that you may be trying to avoid.

Boiler Fuel Type

Do you want a gas boiler that uses natural gas and creates CO2, or something that is powered directly with electricity? Some houses benefit from an eco-friendly system more than others, but there are always risks of any fuel supply being cut off temporarily.

Heat Controls

Will you have the option to adjust the heat levels in your boiler? This won't always be important, but sometimes better customer control options are helpful if you want the extra security of being able to shut off the boiler quickly or at least reduce the temperature.


The overall quality of a boiler isn't just about the installation and how it’s built, but how well it can function for your needs. Sometimes a boiler that's good on paper won't be good in practice, either because of certain technical details or just because your home has a specific kind of heating layout that needs particular boiler features for it to work at its best.


The price of a boiler is always going to be a roadblock for certain people. Some brands, like Alpha, Viessmann and Worcester Bosch, offer higher quality for a higher overall price. This doesn't include the cost of getting installers to set up the boiler or an engineer to service it, either, both things that you'll want to keep in mind.

Finding The Right Boiler

If you're looking for boilers worth trying, here's an easy step by step way to speed up your search.

Look for Quality Brands

Make sure you know brands like Viessmann, Worcester Bosch and Alpha by name and logo. All three make different boilers, but the collective Worcester Bosch, Alpha and Viessmann boilers range is still quite extensive. Take a look at the boilers page of each brand's site and see what they offer.

Know What You Need

Be sure you know what you need from any new boilers you might find. Do you need to heat up multiple bathrooms? Do you want to use a certain type of power or energy? Are you installing it in your loft, or if there isn't room in the loft, does it have to go on the ground floor? This can lead to you the right product for your needs.

Think About Boiler Types

Combination boilers can't support every system, but no boiler type can. A Worcester Bosch combination boiler is still a combi boiler, and a combi boiler still has limits on how it can create hot water even with a constant flow of energy. That combi boiler is also best in the loft, not the ground floor, and a regular combi boiler may not have a decent flue system at all.

Each product is meant for a certain role in a system, and if your system doesn't include that role, then that boiler might not be ideal. Combi boilers can't stand in for conventional boilers well, for example.

Search for Good Product Options

Look at the review rating of each product before it enters your basket. Does the rating give credit to why the product has such a low good?

Rating systems can be hard to work with, and each product usually has a rating per page, so it can be tough to compare a rating from one product to another. Remember that the rating system may promote rating based on how they deliver and the basic functionality instead of the product itself.

Best Central Heating Boilers

Which is the best central heating boiler for 2021?


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Alpha E-Tec 28kw


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Viessmann Vitodens 050-W


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Viessmann Vitodens 050-W


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Viessmann Vitodens 050-W


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Worcester Bosch Greenstar 4000 30kW


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Worcester Bosch Greenstar CDI Compact 28kW


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Worcester Bosch 8000 Style 30kW


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All the prices above are starting from prices, the price may vary depending on your property type and heating demand.

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Stephen Day profile photo
Article by
Stephen Day | Co-founder
Gas Safe registered and FGAS certified engineer with over 20 years experience in the heating and cooling industry.