Gas Boiler Types Explained Re February 3, 2023

Gas Boiler Types Explained

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Do you need your gas boiler type explained?

One of the most common enquiries we get here at WarmZilla HQ is ‘What type of gas boiler do I have?’, followed by ‘What type of boiler do I need?’. A few factors are involved in determining what type of boiler would best suit your needs. This article will look at those factors and help you decide which boiler type is right for your home. We’ll look at the advantages and disadvantages of each boiler type and the impact on the environment each type of boiler has.

When getting a quote on a new boiler with us, we help you to identify what type of boiler you currently have, and if you’re still unsure, you can ask a member of the Operations Team using our live chat option. Not only do we help you identify your current, but we’ll also suggest the ideal boiler type for your home and include the price of transferring from one system to another (i.e. transferring from an old system boiler to a new combi boiler). We would recommend spending a little time familiarise yourself with the different types available and assessing which would be best for you. It’s always good practice to understand the basics for yourself.

With this said, you can now use our Boiler Comparison tool, which allows you to compare up to 3 boilers at one time. You can also compare your current boiler against two other boiler models and brands to help you find the most reliable and energy-efficient boiler for your home. 

Most combi boilers last between 10-15 years, sometimes even longer, so you want to make sure you make the correct decision. Factors involved in the decision include cost, reliability, space it takes up, ability to provide sufficient hot water based on your needs, water pressure in your home and the size of your home.

The three most common types of gas boilers are system, combi and regular boilers (also referred to as conventional, traditional, open vent or heat-only boilers). These boiler systems are all known as ‘condensing boilers‘.

All homes in the UK are legally required to have condensing boilers fitted as they are substantially more energy-efficient than older forms of boilers. Condensing boilers make use of heat that would have escaped into the atmosphere with non-condensing boilers via a fitted heat exchanger. By utilising this heat for your home, condensing boilers are much more efficient, saving you money on your heating bills and lowering your carbon footprint, a double bonus!

If you would like to learn more about how a condensing boiler works, click here.

Now that we have some background let’s look at the three main boiler types used in the UK today. 

Combi Boilers

Combi boilers, or to give them their full title, combination boilers, are the most common type of boilers found and installed in the UK. In fact, over half of all boiler installs in the UK are combi boilers. The name combination boiler comes from their ability to both heat your home and provide you with hot water.

Combi boilers are connected directly to the mains water supply coming into your home. They heat this water directly, eradicating the need for a separate water tank (as with a system or regular boiler). This saves a great deal of space, especially in flats and smaller homes where space is limited.

Another benefit of combi boilers is that they supply hot water at mains pressure, which allows you to enjoy mains pressure showers without needing to install a shower pump.

Combi boilers keep a small reservoir of pre-heated water within them to ensure they can supply hot water to taps instantly. Head over to our ‘how do combi boilers work‘ blog for more details.

Combi boiler advantages

  • Combi boilers are the best option for homes with limited space as they don’t require separate storage tanks. Some combi boilers can even be installed in a kitchen cupboard.
  • Ease of installation. Combi boilers are the easiest type of boiler to install, with most being installed in between 4-8 hours as long as no issues are encountered.
  • Combi boilers are the most energy-efficient condensing boiler as they operate at 90% energy efficiency as a minimum and heat only the water you need.
  • As combi boilers are connected to the mains water supply, you won’t experience sudden pressure drops when turning the taps or shower on.
  • Hot water is heated and supplied on demand, so you won’t ever run out. With a system or regular boiler, once you use all the hot water in the storage tank, you have to wait for more to heat up.

Combi boiler disadvantages

  • As a combi relies on mains water pressure, your water flow may be sub-standard if you live in an area with poor water pressure. Use this flow rate calculator to establish your flow rate.
  • You can’t use power showers with combi boilers as they rely on hot and cold water feed from a gravity-fed system.
  • If your home has two or more bathrooms, a combi boiler may not be ideal as it will struggle to provide hot water to two bathrooms simultaneously.
  • Unlike system and regular boilers, there is no hot water tank, so if your boiler breaks down, you will be without hot water.
  • Only advanced combi boilers are compatible with solar energy.

Do you want to know more about the best combi boiler brands in 2022? Click the link for a separate blog (cheeky self-promo!)

System Boilers

System boilers can usually be found in homes with high hot water needs. They work by heating water in a separate storage tank from the boiler, usually found in an airing cupboard. This hot water is available for use in multiple bathrooms should it be required. In practice, you can have two baths running in separate bathrooms, and they will both get hot water without affecting your home’s heating.

A system boiler differs from a combi in that a combi heats water directly from the mains supply and doesn’t store hot water, so you may struggle to run two baths simultaneously.

System boiler advantages

  • Ideal for homes with 2 or more bathrooms
  • Relatively easy to install
  • Doesn’t require a cold water tank
  • Compatible with solar thermal energy

System boiler disadvantages

  • Large storage tank required, not suitable for flats or smaller homes
  • Loss of heat from the hot water storage tank, no matter how well insulated
  • Hot water is limited to the capacity of the storage tank. Once the hot water from the tank is used up, you will have to wait for it to heat the water again. A combi boiler heats water straight from the mains, so it will always be hot.

If you would like more information about the best system boilers on the market, this blog may help. 

Regular Boilers

Regular boiler systems, also known as conventional, traditional, heat only or open vent boilers, are the most difficult to install or replace.

A regular boiler includes a hot and cold water storage tank, the boiler itself, and an expansion cistern next to the cold water tank. This takes up quite a bit of space in a home, and it’s usually preferable to switch to a combi so that these tanks can be removed.

Regular boilers are becoming less and less common as they are replaced with more efficient boiler systems that don’t take up as much space and have fewer parts, meaning there is less to potentially go wrong.

Most likely, you would only tend to keep a regular boiler system if you were concerned that your central heating system would struggle to cope with the increased water pressure from a system or combi boiler.

Similar to system boilers, regular boilers are able to supply large amounts of hot water simultaneously to multiple bathrooms due to the hot water storage tank facility.

Regular boiler advantages

  •  Regular boilers can supply hot water to two or more bathrooms simultaneously and won’t affect water pressure or heating.
  • An immersion heater can be fitted to the hot water tank to ensure you can still get hot water in the case of a boiler breakdown.
  • Regular boilers are suitable for homes that suffer from low water pressure.
  • Compatible with solar energy sources in the same way as a system boiler.

Regular boiler disadvantages

  • The amount of space the boiler and tanks take up is impractical, particularly for smaller homes or flats.
  • Limited hot water up to the volume of your hot water storage tank.
  • A hot water tank loses heat, no matter how well insulated.
  • Difficult to install, only suitable as a replacement for another regular boiler system.
  • Are you interested in getting a regular (heat only) boiler but unsure which model is best for your home? Look no further! We have a Best Regular Boiler 2021 blog which is helpful!

You should now be able to identify what boiler type you currently have. If you still aren’t sure, then please contact us.

Which Boiler Type Do I Need?

The boiler type you need depends on the size of your house and the water pressure in the area you live in.

A combi boiler will be the best solution if you have one bathroom or even two bathrooms (one with an electric shower).

If you have two bathrooms that are often used simultaneously, like getting ready in the morning, you may be better off with a system boiler, as there should be plenty of stored hot water.

If you have a regular boiler and an old central heating system, replacing it with an updated regular boiler might be your best option.

When it comes to choosing the correct size boiler for your home, there are a few things that are important to consider. These include:

  • Total number of radiators in your home 
  • Total number of bedrooms
  • Total number of bathrooms
  • Number of people living in the property

Once you’ve gathered all this information, you should then be able to identify what boiler size you need.

We have a separate blog that covers this if you want more information about the what kW output you need for your home

The below table will help you find the boiler size for your home.


Table 1 : Boiler Size Recommendation

 Flat/small houseMedium houseLarge house
RadiatorsUp to 10Up to 15Up to 25
Approx. boiler size24kW – 27kW28kW – 34kW35kW – 42kW

Gas Boiler Alternatives

You may have heard a lot of talk in the news lately about gas boiler bans, hydrogen boilers, insanely expensive heat pumps, and rising fuel costs. If you’re a homeowner with an old boiler, you’re probably getting a lot of conflicting advice on what you should do. So what are the alternative options to your trusty gas boiler?

Hydrogen Boilers

As of late 2021, you cannot buy a hydrogen boiler. As there is no hydrogen fuel supply currently going through the gas grid, there wouldn’t be any point in owning a hydrogen boiler.

Worcester Bosch, Ideal, Baxi, Vaillant, and Viessmann have all created ‘hydrogen-ready’ boilers. A hydrogen-ready boiler is a system that can operate on natural gas and then be converted by a qualified engineer to operate safely and efficiently on hydrogen within an hour. Worcester Bosch has called for all boilers installed after 2025 to be hydrogen ready, so when/if the time comes to switch to hydrogen – the U.K will be ready.

Hydrogen-ready boilers are slightly different from ‘hydrogen blend ready’ boilers. Hydrogen blend-ready boilers are able to run on a blend of 20% hydrogen and 80% natural gas blends of fuel.

Ideal, Baxi, Worcester Bosch, and Vaillant have already built hydrogen boilers which are currently being tested in real-life simulations. These hydrogen boilers will be sold as ‘hydrogen ready’ boilers when they pass the testing phase.

There is no set date when you can buy a hydrogen-ready boiler, but they could be available from 2026; however, there are still hurdles for hydrogen boilers to face before they are ready for widespread adoption.

Heat Pump

One thing to keep in mind with heat pumps is that they are not a new technology. In fact, the first heat pump system was designed in 1855, with the first ground source heat pump following in the late 1940s.

Mr Kwarteng, secretary of state for business has stated that “Heat pumps are already a predominant technology in some other countries and have high levels of customer satisfaction”. So why hasn’t this technology been widely adopted already, and why are we only hearing about heat pumps now?

However, there are reasons why heat pumps haven’t been widely adopted, despite being an environmentally friendlier option than natural gas, including cost, difficult installation, a shortage of skills engineers to install the heat pumps and suitability for homes, especially smaller homes. If you want to learn more about the current Gas Boiler ban or whether or not Heat Pumps or Hydrogen Boilers will replace Gas Boilers, head on to our other blogs. 

If you’re still unsure what boiler is the most suitable for your home, why not try our Boiler Comparison tool? This tool allows you to compare up to three boiler models or brands at one time so that you can see the difference in efficiency, dimensions, warranty and features.

For most cases, a combi boiler is the best solution, as you might expect, given that half the boiler installs in the UK are combis. They are extremely energy-efficient, easy to install and take up significantly less space than system and regular boilers.

As they are easier to install, they also cost a lot less, with prices starting from £1,650 on the WarmZilla website, including installation, 10-year guarantee, smart thermostat and a system filter.

Every home will be different, but hopefully, with the information in this article, you are better informed to decide for yourself what boiler type would suit your needs best. If you still aren’t sure, please contact the team.

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