What is the best system boiler to buy in 2024?

A new boiler is a significant investment that should provide you with household hot water and heating for over a decade. That means that it’s essential to get it right so that your needs are met without any worry or stress.

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The choice is a great thing, but sometimes it can feel overwhelming. There are so many boiler brands, and each one has a range of system boilers.

What makes a good system boiler?

Nowadays you may have heard about the importance of the boiler’s efficiency level and also ensuring that the system is future-proof with the introduction of hydrogen mixes as the source of fuel.

And that’s not to mention the current choice between an oil boiler, gas, LPG or even an electric boiler. It’s no wonder that trying to understand all the different boiler types can seem like a complete nightmare.

The best system boilers on the market right now

So, this is where we step in to help. We’ve done the hard work for you and looked at dozens of system boilers before narrowing it down to what we think are the four best boilers currently available.

1. Viessmann Vitodens 100-W
2. Worcester Bosch Greenstar 4000 System
3. Worcester Bosch Greenstar 8000 Style
4. Ideal Logic+

We’ll also provide you with a breakdown of why they’ve got onto our shortlist and what type of household they’re the best fit for.

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Best system boilers reviews

Finally, we get to present to you our selection of the best system boiler range in the UK. We assessed a whole range of boilers on a whole range of criteria, including functionality, efficiency levels and how future proof each one is.

Now is your opportunity to review our shortlist and compare boilers for the best fit for your home.

#1 System Boiler – Viessmann Vitodens 100-W

The Viessmann Vitodens 100-W is the brand’s top-selling gas boiler and it’s been updated for 2021. This is a boiler well known for being discreet. It’s compact and so quiet that it can be installed in a kitchen and not be intrusive while it’s operating.

Key features

Stainless steel heat exchanger

The 100-W features the Inox-Radial stainless steel heat exchanger. Corrosion-resistant and incredibly durable, the stainless steel inox-Radial is responsible for converting the natural gas into heat.

MatriX Plus burner

This highly efficient burner has exceptionally low pollutant and noise emissions. It too is made from stainless steel giving high levels of performance and long working life.

Lambda Pro combustion control system

A Viessmann innovation, the Lambda Pro combustion control system ensures that there is a continuously clean and efficient combustion process no matter the type of gas being used.

Recommended setting

Could this be the best boiler for you? Well, the manufacturers have suggested that the Viessmann Vitodens 100-W can comfortably heat smaller homes that are already well insulated.

Power output options

The Viessmann Vitodens 100-W is available in four different power outputs, 19, 26, 30 and 35 kW.

Efficiency levels

Achieving an amazing 94% efficiency means that just 6% of the energy used to provide the hot water is lost during the healing process. With those sorts of figures, you should be able to make some good savings on your energy bills especially if you currently have an older boiler.

Is it hydrogen compatible?

Viessmann boilers are leading the way with the majority of their range of gas boilers already being 20% hydrogen compatible. The Vitodens 100-W is no exception. It requires no further adjustments to be able to use a 20% hydrogen mix as its source of fuel.

Solar compatible?

All Viessmann boilers are 100% compatible with solar thermal panels. The Vitodens 100-W has an added advantage here because it also has what’s called boiler suppression. That means that whenever solar power is available, the boiler will always use that first. The boiler will only fire up using gas when it’s absolutely necessary.

That means that there are significant savings on energy bills when using this natural source of energy.

Guarantee period

The Vitodens 100-W comes with a five-year warranty as standard but this goes right up to twelve years when a Viessmann trained engineer undertakes the installation.

Getting the best combi boiler with a long warranty period is the best solution if you do not want a system boiler.

Smart thermostat options

Viessmann has its own smart thermostat system called Vicare. This then means that you can control and programme the 100-W from an app on your mobile phone. And if there are any problems with your system boiler or central heating, then the app will send an alert both to you and to your nominated heating engineer.

Looking for more information on this boiler? You’ll find it in our Viessmann 100 review.

#2 System Boiler – Worcester Bosch Greenstar 4000 system

While the Worcester Bosch Greenstar 4000 may have one of the longest names, this is not your usual white box style of the boiler. It’s available in black and white and its stylish design will mean that you won’t want to hide it away out of sight. With a whole range of features and options, this was an easy inclusion in our selection process for the best boiler.

Read more: Worcester 4000 review

Key features

Quiet operation

This is the quietest system boiler in the range and has achieved Quiet Mark Accreditation. So, if peaceful surroundings are important to you, then the Worcester Bosch Greenstar 4000 could be a strong contender for your new boiler.

Modulation of 1:10

Modulation is the ability of a boiler to ‘turn down’ its output. So, if you had a 20kW boiler but you only actually need 10kW of pour over the next hour, the boiler turns down its output for the next hour.

Before modulation was an option, that 20kW boiler would have come on for 5 minutes and then turned off for 5 minutes all the way through that hour.

This was an incredibly wasteful system. It also wears out the mechanical parts much quicker and the system tended to run very hot.

The Worcester Bosch Greenstar 4000 has a modulation of 1:10 so that means that it can drop right down to 10% of its output as needed.

Wireless operation with Bosch EasyControl

With an internet-connected thermostat, you have quick and easy control of your heating and domestic hot water system. This app has been specially designed for Worcester Bosch boilers and it makes it incredibly easy to create the perfect environment for you and your family.

Now you can set the times and temperatures that you’d like for each room in the home. No more having the bedroom too hot because you need the rest of the house to be warm first thing in the morning.

Recommended setting

Worcester Bosch suggests that this is the best boiler for small to medium-sized homes with one bathroom.

Power output options

There are five different power output options: 12kW, 15kW, 18kW, 21 kW and 24kW

Efficiency level

The Greenstar 4000 achieves 94% efficiency levels which gives it an ‘A’ ErP rating.

Is it hydrogen compatible?

The entire Worcester Bosch range of boilers are able to run on a 20% hydrogen, 80% natural gas mix. This then gives peace of mind that they’ll be able to cope with any future changes to the national gas grid and its supply of fuel.

Solar compatible?

The Worcester Bosch Greenstar range is compatible with their Greenskies solar panels which can then provide you with energy and cost savings.

Contrary to popular belief you don’t need to have blazing sunshine every day to be able to benefit from solar panels! However, with the Greenskies you have the backup of a natural gas boiler should the weather take a turn for the worse.

Guarantee period

A ten year guarantee period is offered on the basis of the initial boiler installation being undertaken by a Worcester Accredited Heating Engineer.

#3 System Boiler – Worcester Bosch Greenstar 8000 Style

Based upon the Worcester Bosch Greenstar boiler range, this is their top of the range system boiler. It has the same sleek styling as the 400 and is also available in either black or white.

If you need a system boiler that can cope with the demands of a busy household, then this could be a good option.

Recommended setting

The Worcester Bosch Greenstar Style range is an excellent fit for homes of all sizes and it can comfortably cope with meeting the heating and hot water needs of a large home with multiple bathrooms.

Power output options

The system boiler range is available in two different power output options of 30kW and 35kW. This is also a range that’s also available as a combi boiler which offers output options from 30kW right up to 50kW.

Efficiency level

Both power output options within the Worcester Bosch 8000 range have been assessed as having an ErP rating of ‘A’ making them some of the most efficient gas boilers.

Is it hydrogen compatible?

As already mentioned, all boilers from Worcester Bosch are hydrogen ready. That means that they can run on a hydrogen/gas mixture without needing any further alterations.

Solar compatible?

Just as with the 4000 model, the 8000Style is compatible with Worcester Bosch’s Greenskies solar panels.

Guarantee period

Up to a 12-year guarantee is available as long as the installation was carried out by a Worcester Accredited Installer. Do also make sure that the annual service is carried out by a heating engineer who is on the gas safe register.

For even more information, take a look at our Worcester Bosch 8000 review.

#4 System Boiler – Ideal Logic+

Quick and easy installation

With the boiler, weight starting at just 26kg and it fitting neatly into a kitchen cupboard, the Logic+ is a favourite of gas engineers for its quick and easy installation.

LPG conversion kit available

If you’re not able to get gas, LPG could be an alternative solution for your heating system. An LPG conversion kit is insatiable for the Logic+ on the 30kW boiler model.

Range of flueing options

If your home doesn’t fit neatly into standard flue options, then the process of finding a suitable new boiler can be a nightmare and very expensive. The Logic+ comes with a wide range of flue options meaning that those exhaust gases can be quickly and easily dispensed with.

Recommended setting

Depending on which power output you go for, this range of system boilers is suitable for a wide range of home settings from smaller properties right up to large homes with multiple bathrooms.

Power output options

This range of boilers are available in four different power outputs, 15kW, 18kW, 24kW and 30kW

Efficiency level

The Logic+ system boiler has an ErP rating of ‘A’. This is also an Energy Saving Trust endorsed boiler meaning that there’s a real opportunity to save money on your energy bills

Is it hydrogen compatible?

This is a hydrogen ready boiler so no work will be needed for it to be able to cope with a 20% hydrogen mix. Hydrogen boilers are readily available in the UK.

Solar compatible?

Ideal makes no mention of solar compatibility on their website. However, that doesn’t mean to say that it can’t be done. If it’s an important part of your heating strategy, then a quick call to their customer service helpline will be able to provide all the information you need.

Guarantee period

Ideal offer a 7-year parts and labour warranty on this model. Do make sure though that the new installation is registered within 30 days and that you have the boiler serviced annually. You should look up the boiler service cost before you book it to make sure you know how much it could be and what is included.

The heat exchanger on the Logic + is covered by a separate 10-year warranty which is factored into the new boiler cost when buying the boiler.

How do the top system boilers work?

A system boiler takes its cold water feed directly from the mains supply. The water is then heated through the energy transferred from the gas jets, and that takes place within the heat exchanger.

The heated water is then forced through to the hot water cylinder or hot water tank, where it’s stored, ready to call upon, for your heating and hot water needs.

Unsure if you definitely need a system boiler, find out in our combi vs system blog here.

Advantages of a system boiler

The key advantage of the system boiler is in that hot water tank meaning that you have a large supply of domestic hot water ready to use.

That makes them the best boilers for homes that have high hot water demands. So, that might mean that you need to have a supply of hot water to multiple taps or showers at exactly the same time.

If you currently have a system boiler, then the installation of a new boiler of the same type is going to be a quicker and cheaper option than going for a different kind of heating solution.

Disadvantages of a system boiler

The key benefit of the system boiler, being able to store hot water, can also be the cause of its disadvantages. That’s because first of all, you need the space for the hot water cylinder, and secondly, there is going to be some heat loss while the hot water is being stored.

Finally, once the cylinder of pre-heated water has been used, you’ll then need to wait for more to be heated before you get a further supply of hot water.

While it does have considerable hot water capabilities, if you have a large family and multiple bathrooms, then the last person in the shower might not find that the water is all that warm.

System boiler vs conventional boiler

Another option to a system boiler is a conventional boiler, or as it’s sometimes known, a regular boiler or heat only boiler. As well as the hot water cylinder, the conventional boiler also needs a cold water tank that feeds the water to the boiler itself.

Advantages of the conventional boiler

One advantage of heat only boilers is that an immersion heater can be installed inside the hot water cylinder. That then means that if the boiler breaks down, you still have a way of generating hot water.

Additionally, if you already have a heat-only boiler then often the best boiler replacement quote option is to replace it with the same type of heating system. It may well be, for example, that the hot water cylinder is absolutely fine and you just need a new boiler installed.

Disadvantages of the conventional boiler

Just as with the system boiler, heat only boilers have the same issue with heat loss through having a hot water storage cylinder. Then there’s also the need to reheat a tank of water once the stored supply has been used.

A heat-only boiler is also much more complicated in its set-up when compared to a system boiler. And with more components, such as the cold water storage tank, that means that there’s more that can go wrong too!

System boiler vs combi boiler

The combi boiler can both heat your home and provide hot water all from one unit. So that means there is no need for a hot water cylinder or a cold water tank.The best combi boilers are the most popular choice in the UK, but that doesn’t mean to say that they’re the right heating system for everyone or for every situation.

Advantages of the combi boiler

That small size of combi boilers makes them an appealing option for small homes and apartments. All you need is to get the boiler installed, there’s no need for water tanks or cylinders.

The other key advantage to the combi boiler is that they provide hot water on demand, so that means that there is no risk of running out of stored hot water.

Disadvantages of a combi boiler

The combi boiler does, however, struggle to meet the demands of busy households.

If the hot water tap is turned on in the kitchen while someone is having a shower, then they may find that nice hot shower suddenly becomes very cold.

Another consideration of the suitability of a combi is the mains water supply. If it’s not high, then the combi boiler may struggle to provide hot water to radiators and taps that are any distance from the boiler itself.

If you’re now wondering if this might be the best boiler for your heating needs, then you can get a new boiler quote for a range of combi boilers in just a few minutes

What size system boiler does my central heating need?

As you look through our list of recommended system boilers, you’ll see information on the different power outputs available for that model. So, it makes sense to quickly mention how to work out which size boiler you need to look for.

The size of the boiler is measured in kilowatts (kW) rather than the physical size of the unit. A kilowatt is a measurement used to define how much energy, in the form of heat, is output by the boiler.

The more heating and hot water needed then the higher the output you’ll need to meet that demand. Now there are some other factors to consider by kW is a good basic measure.

Number of radiators in the home

One of the key factors that will determine the size of the boiler that you need is the number of radiators within your heating system.

A small flat with a few radiators

If you live in a small apartment with very few radiators, then an entry-level boiler is likely to be sufficient to meet your needs. You’re probably not going to need or even have the space for the cold water tanks or hot water cylinders of conventional and system boilers.

Average three or four-bedroom house

This size of home usually has around ten central heating radiators and so will need a small or medium boiler of between 24-30 kW.

Larger three or four-bedroom house with an en-suite bedroom

For a larger house with higher heating needs or an en-suite bathroom, then a boiler in the range of 30-35 kW is likely to be needed.

Large house with 20 radiators

For larger properties with as many as 20 radiators or multiple bathrooms then you’re going to need a 35-42 kW to be able to comfortably meet the heating needs of the home.

This is also the type of property that combi boilers are going to struggle to supply sufficient heat and hot water to; a system boiler is likely to be a much better fit.

Should I choose an oversized boiler?

Modern condensing boilers are much more efficient than they used to be. So, the old advice to get a larger boiler than you need to compensate for heat loss is no longer recommended.

In fact, having a boiler that’s larger than your heating system needs is going to result in wasted energy and higher energy bills.

Future-proofing your system boiler

Under the government’s current plans, new build homes will not be able to have a gas or oil boiler fitted after 2025. Electric boilers will still be an option but these are notorious for their high running costs.

So, this doesn’t mean that you won’t be able to get a replacement gas boiler for your older home. But it is worth understanding what the future changes are likely to be so that you can ensure that your new system boiler is able to cope with them.

Hydrogen ready system boilers introduction

Over the next five years, there are plans to introduce hydrogen to the gas grid. Most modern boilers are able to work perfectly well with a 20% hydrogen/ 80% gas mix and that’s exactly what the first phase of the transition is likely to be.

There are still some challenges for the manufacturing industry to overcome in achieving hydrogen production at the levels needed along with resolving storage and distribution issues. It’s thought that it will be at least another ten years before the pure hydrogen boiler is a viable alternative to a natural gas boiler.

Worcester Bosch and Baxi are currently leading the field in hydrogen heating solutions as they have already developed a 100% hydrogen-ready boiler.

Best system boiler manufacturers

We mentioned earlier that part of finding the best system boilers is also to look at some of the best boiler brands. Our top system boilers come from three different manufacturers, Viessmann, Worcester Bosch and Ideal.

So before we leap to look at our top four boilers, now’s the time to find out a little more about these three boiler brands.

Viessmann system boilers

The Viessmann Group is one of the top names in the world of heating and boiler systems. They’ve been operating for over a hundred years, and now have an impressive workforce of over 12,000 employees. With a 3-billion-euro annual turnover, it’s easy to see how many homeowners consider them to have the best boilers on the market.

In the UK, Viessmann is based in Telford, where the sales, customer service and technical support teams are based. Outside of the UK, Viessmann operates in over 120 countries which very much makes this a global organisation.

Viessmann has been awarded the coveted Which? Best Buy status for their Vitoden range of boilers, and they have an impressive score of 4.6 on Trustpilot, from verified customers. This then classifies the company as excellent in both the service they provide and the quality of products sold.

 Worcester Bosch system boilers

Originally known just as Worcester, this boiler brand is a relatively new entry to the heating market having been set up in the 1960s. However, their impressive products soon caught the eye of the Worldwide Bosch Group, which they became part of in 1992. Then they became known as Worcester Bosch.

Worcester Bosch is the UK market leader for home boilers and is often acknowledged as the best boiler brand. So, it’s probably not too surprising that we have two of their system boilers within our shortlisted selection.

The company still has their headquarters in Worcester with its customer service teams being based there along with the gas boiler manufacturing plant. Oil boilers are produced at the company’s site at Clay Cross in Derbyshire. 

Just as with Viessmann, Worcester boilers reviews receive a healthy score of 4.6 on Trustpilot. With over 25,000 reviews, that’s an impressive average to maintain.

Ideal system boilers

This is a boiler brand with fantastic experience within the heating market. Founded in 1906 their early innovations made a boiler installation a real possibility for working-class homes. Since then they have continued with the innovative approach to the central heating boiler.

In 2009 their Logic range of boilers achieved efficiency levels of over 90% which cemented Ideal’s place as a top boiler brand.

Ideal Boilers are based in Hull and their field engineers are located around the UK, ensuring a rapid response should there be any problems.

As for their Trustpilot reviews, well Ideal are out ahead with an amazing score of 4.8; that means an awful lot of customers who are very happy with their new boiler from Ideal.

Best system boiler roundup

Despite the trend for moving to a combi boiler, system boilers still have a niche to fill. Whether you’re looking for gas, LPG and oil boiler or even an electric boiler, there is an option perfect for your heating needs.

Even though we think our four choices are great options, there of course many other system boilers that are great options. Ariston boilers, the Vaillant Ecotec plus and models from Alpha are all worth looking at. If we had room for one more boiler then that would probably be taken by the Vaillant Ecotec, which with Vaillant boiler service, can be an efficient and reliable system boiler for years.

If you’re now wondering how much system boilers cost, then this is when getting new boiler quotes is a great next step.

By simply entering a few details about your heating requirements and domestic hot water needs, you’ll be presented with a range of boilers that are a perfect fit for your home.