The Best System Boilers in 2021

The best system boilers in 2021

Investing in a new boiler can set you back a considerable sum of money so it’s important to research your options thoroughly before you buy. 

With so many boiler varieties on the market today, choosing the best fit for your property can be a daunting task.

That’s why we’ve developed our own, 100% unique and official online boiler ranking system so you can compare choices before you purchase.

In this article, we take a closer look at the best system boilers available in the UK in 2021 and, to give you better background knowledge, we also discuss:

• what is a system boiler
• why gas-powered system boilers are better
• what size of boiler is best for your home
• the top 10 gas system boilers on the market right now
• choosing a gas system boiler for a smaller property
• the best 5 gas system boilers for a medium sized properties
• gas system boilers to consider for a larger property
• the best oil-powered system boilers
• the best electric system boilers

Here at HomeSage we can help you save up to 54% on the price of your new system boiler and installation.

Simply fill in a form anywhere on this page and one of our suppliers will be in touch shortly with a 100% free, no obligation quote!

What is a system boiler?

Used to heat your water and provide your house with central heating, a system boiler is a closed system with an internal hot water storage cylinder. 

It draws water from the mains supply, heats it using a heat exchanger, and then stores it for future use.

System boilers are often mistaken for traditional boilers.

However, they don’t require the cool water storage tank that traditional boilers need instead they store the water within the self-contained unit. 

The problem with system boilers is that if you run out of hot water, you need to wait for it to heat up again.

This is unlike the more popular combi boilers that keep a constant flow of hot water coming through the taps and radiators.

However, system boilers can be effective in larger houses where there is a high demand for hot water and also for properties located in areas of low water pressure. 

Gas, electric, oil, or LPG – why gas is best

There are four different ways of fuelling your central heating. Depending on where your property is located, you may not have the choice of your preferred fuelling option and it’s recommended you ask your boiler installer for your best option.

Electricity is the most expensive way to heat your home. Although it doesn’t require complicated pipework and is relatively simple to install, your annual energy bills will be high. 

If your property isn’t connected to the mains gas grid, you usually have the choice of two alternative options, excluding electricity.

You can opt for liquid petroleum gas (LPG) which is a touch more expensive than regular gas and requires a storage tank and regular top ups from a supplier.

Heating oil is the final fuelling option, although it is slowly but surely being phased out of use in the UK. 

Much like with LPG, heating oil requires a storage tank and regular supplies from an oil provider – this can be problematic if there are issues getting the oil to you, for example during bad weather or road closures.

Gas is the cheapest way to heat your home and once your property is connected to the gas mains, you have a constant supply of fuel and don’t need to worry about it running out. 

This table indicates the cost of the four main fuel supplies for your central heating.

Please note, the above figures indicate that whilst a 30kW LPG, oil, or gas boiler may be suitable for a medium-sized property, an electric boiler for this size home would only require an output of approximately 12kW.

This means that the figure for a 30kW boiler using electricity is much more likely to be around £1.92 in reality.

Most boiler installer companies will recommend you choose a gas fuelled boiler for your home due to their economic advantages and relative price points.

It may cost you a substantial amount to upgrade your boiler but, if you are choosing a much more energy efficient model, you gain the money back in lower energy bills over the space of a few years. 

We have more information specifically on gas boilers in our gas boiler guide.

Choosing the best right sized system boiler for your home

To make sure you are only paying for the energy you really need, you should opt for a boiler with the correct output for your property size.

Boiler output is measured in kilowatts (kW) and this figure tells you how much it costs to run. 

To work out the equation, you multiply the boiler output by the price of a unit of energy so for example, a 35kW boiler using gas priced at 4p a unit would cost £1.40 to run.

Here, we have composed a table of required boiler outputs for homes of different sizes. 

As a general rule, it depends on the number of radiators in the property and how many bathrooms you have, as well as your average hot water usage.

Choosing a boiler with an output too low for your needs may result in a struggle for hot enough water fast enough whereas if your output is too high your utility bill will be unnecessarily expensive. 

The age of your property should also be taken into account because it may affect the level of insulation you have in your home.

If you have a new property that was built after the year 2000, you should have a very good level of insulation so your heating bill should be as low as possible.

For properties that were built mid-20^th century, for example in the 1950s, the insulation level will be moderate, meaning you are likely to experience some heat loss.

Homes that were built pre-1900 will likely suffer from poor levels of insulation so you can expect to pay more to keep your house cosy. 

System boilers don’t need to worry about water flow rate because they operate with a water storage tank.

This means that as long as the tank has hot water inside, you benefit from a strong and powerful flow of hot water and it isn’t affected if more than one person is using the hot tap at any one time. 

An issue arises once the hot water has been used up as you then need to wait for the storage tank to heat up again.

The best 10 system boilers on the market right now

We think it’s essential to research your boiler options before you make a purchase.

Here at HomeSage, we have developed our own original and unique boiler ranking system in order for you to make the best boiler choice for you.

Choosing a new boiler can be tricky when there are so many different manufacturers, models and specifications to choose from. 

Our boiler scoring system takes the following aspects into account:

• the energy efficiency rating,
• the price,
• the length of warranty available, and
• genuine customer reviews and ratings on Trustpilot.

As you can see from the results, Worcester Bosch have dominated the results in 2021 due to their high energy efficiency ratings and long standard warranties. 

Now follows our top 5 system boilers for each property size – select which one suits your property!

• best system boilers for small properties
• best system boilers for medium-sized properties
• best system boilers for large properties

All our featured boilers below are condensing boilers, which are the most efficient you can get.

The best gas system boiler for a small property

For smaller apartments and terraced properties with 1-2 bedrooms and a single bathroom, you will require an output of up to 27kWif you opt for a gas system boiler .

Currently on the UK market there are 135 boilers in this category and the average price is £961.

As you can see in the table below, Worcester Bosch dominates this division due to their high efficiency ratings, generous warranties and good relative price point.

Worcester Bosch Greenstar 9i Boiler (91.59%)

The Greenstar range are Worcester Bosch’s most popular system boilers and the 9i is the lowest output available in the series.

The Worcester Bosch Greenstar 9i comes with a 7-year guarantee as standard. 

The dimensions of this boiler are 710mm x 400mm x 330mm and is it a wall-hung unit in a traditional white gloss casing and concealed display panel. 

It features simple user controls with a wide range of options to suit your heating and hot water needs.

Worcester Bosch Greenstar 12i Boiler (91.57%)

For those needing slightly more power, the next step up in the Greenstar range is the 12i boiler. 

This model measures 710mm x 400mm x 330mm and features the same gloss white finish as the other Greenstar boilers.

It can be used in conjunction with the Greenstar Solar Panels for increased energy savings and a decreased environmental footprint. 

This boiler has a grade ‘A’ rating in energy efficiency and comes complete with a 7-year warranty.

Worcester Bosch Greenstar 15i Boiler (91.42%)

As with all Worcester Bosch Greenstar boilers, the 15i comes complete with the Royal seal of approval – as Worcester Bosch have received a Royal Warrant for supplying their boilers to the estates of Her Majesty The Queen.

This particular model measures in at 710mm x 400mm x 330mm and comes with the standard 7-year guarantee providing you follow the terms and conditions.

The Worcester Bosch Greenstar 15i boiler is suited for small homes that require a little more power to heat.

This boiler is a traditional-looking white boiler with a fold-down display cover and is front-access, meaning any servicing or maintenance will be easy for your engineer.

Worcester Bosch Greenstar 18i Boiler (91.29%)

One of Worcester Bosch’s most popular boilers, the Greenstar 18i has the same dimensions as the other ranges of output in the series – 710mm x 400mm x 330mm.

This boiler features a large ‘Condensesure’-style siphon that has been built directly into the boiler and therefore eliminates any risk of frost damage to the pipes if it is installed in a garage or loft.

This system boiler rates an ‘A’ for energy efficiency so you know your heating bill will be considerably lower than those of subordinate ratings.

Worcester Bosch Greenstar 21i Boiler (91.26%)

The final option for gas system boilers for small properties in the Greenstar range is the Worcester Bosch Greenstar 21i boiler.

The dimensions of this boiler are 710mm x 400mm x 330mm and features an LED display screen concealed behind a flip-down panel.

This boiler has a low energy pump so your electrical usage will be reduced and it is also compatible with the range of Greenskies Solar Panels. 

Best choice of system boilers for a medium sized property

For semi-detached or larger terraced homes with 3-4 bedrooms and 1-2 bathrooms, your choice of system boiler should range between outputs of 28kw – 34kW depending on your average heating requirements.

As of 2021 there are 31 system boilers available in this category and the average price is £944. 

Worcester Bosch Greenstar 30i Boiler (91.07%)

This higher output Greenstar boiler comes complete with a 10-year guarantee providing you follow the required terms and conditions regarding annual services and installation.

The dimensions of this boiler are 690mm x 390mm x 280mm, so it is compact in size and suitable to be hidden away out of sight in a cupboard or kitchen unit.

This boiler is lighter than other models by Worcester Bosch and weighs just 31.7kg.

It features compatibility with the Greenstar Solar Panels and comes complete with The Royal Warrant.

Worcester Bosch Greenstar 8000 Life 30kw Boiler (90.78%)

One of the newest models in the Worcester Bosch catalogue, the Greenstar 8000 Life 30kw boiler boasts a modern aesthetic and a range of advanced technological features for ease of use.

The dimensions of this boiler are 780mm x 440mm x 365mm and weighing in at 53kg is slightly on the larger size.

It has a steel-reinforced casing cover that can be removed with just one screw, meaning no fiddling about for your engineer during your annual service. 

This boiler has a pleasing design featuring a fully digital circular LED control panel with user-friendly settings.

Worcester Bosch Greenstar 8000 Style 30kw Boiler (90.59%)

This top of the range boiler boasts innovative features to keep your house warm and cosy at a minimal cost to you and the environment. 

The Worcester Bosch Greenstar 8000 Style 30kw measures 780mm x 440mm x 365mm and is available in either gloss white or gloss black so you can make the perfect choice to match your interior design aesthetic. 

With an efficiency rating of ‘A’ you can be sure your energy bill will come in at a considerably low amount. 

It has a full colour LED system control screen that makes programming your heating needs easy.

Baxi Megaflo 28kw Boiler (90.06%)

If your home has a high demand for hot water, the Baxi Megaflo 28kw could be worth considering. 

It boasts a 7-year warranty as standard for extra peace of mind and is built in the UK using high-quality brass components for longevity.

The dimensions of this wall-hung boiler are 780mm x 450mm x 345mm and it has a durable white casing complete with stylish chrome trim and smart Baxi logo.

This boiler scores highly for energy efficiency and rates as an ‘A’ so you know you will pay less for your heating needs even during the cooler months.

Baxi Megaflo 32kw Boiler (89.98%)

The next output level up in the Baxi Megaflo range is the 32kW model.

This boiler shares the same dimensions as the lower output model, measuring 780mm x 450mm x 345mm and it features the same minimal design with a concealed display panel and chrome trim. 

The Baxi MegaFlo 32kW system boiler would suit a medium sized property with high hot water needs and could work well in an area of low water pressure.

As with most Baxi boilers, this model is front-access for ease of installation and maintenance. 

System boilers to consider for a larger property

If your property is a larger home with 4+ bedrooms and 3+ bathrooms, you should consider a system boiler of 35kW or above.

There are currently 18 boilers in this category and the average price is £1,445.

Worcester Bosch Greenstar 8000 Life 35kw Boiler

Another top of the range boiler from Worcester Bosch, the Greenstar 8000 Life 35kw is over £100 cheaper than the average UK large property system boiler.

This range of boilers was built upon the award winning Greenstar CDi classic series but has been designed to look and feel far more modern, housing a range of advanced technological features for maximum usability. 

It measures 780mm x 440mm x 365mm, is available in a luxurious gloss white finish and is compatible with the Bosch EasyControl system for heating control on the go. 

Worcester Bosch Greenstar 8000 Style 35kw Boiler

If you liked the sound of the Greenstar 8000 Life 35kW but want something a little bit different, look no further than the Greenstar 8000 Style 35kw system boiler which is available in both gloss white and gloss black. 

It has slightly different dimensions, standing tall at 824.95mm x 364.6mm x 440mm.  

This boiler boasts a full colour LED system control panel housed in a unique circular display, and the boiler itself has a sturdy scratch free finish. 

The condensate trap on this boiler can be easily removed for quick cleaning which reduces the risk of freezing pipes, so you don’t need to worry if you install this boiler in the loft or garage.

Vokera Evolve S 35kw Boiler

The state-of-the-art boilers in the Vokera Evolve S range boast easy installation, high energy efficiency rates and an easy to use text driven menu.

This model measures 740mm x 420mm x 350mm and is manufactured in Poland.

If you install this boiler with a BeSMART engineer who is registered with the Vokera Affinity you can benefit from a full 10-year warranty, otherwise you can get a 7-year warranty as standard.

This boiler has a built-in carbon-monoxide monitor for extra peace of mind. 

Viessmann B1HC Vitodens 100-W 35kw Boiler

This system boiler from Viessmann measures 700mm x 400mm x 350mm and is a fairly low weight at 37kg.

Not quite as energy efficient as the equivalent output Vokera boiler above, the Viessmann B1HC Vitodens 100-W 35kw boiler has a rating of ‘B’. 

If you have this boiler installed by a registered Viessman engineer, you can benefit from a full 10-year warranty, otherwise you have a standard 5-year warranty should anything go wrong.

This boiler features a backlit LED touchscreen control panel with constant temperature control for your property and weather compensated operation for reduced energy costs. 

Viessmann B2HB Vitodens 200-W 35kw Boiler

This is one of Viessmann’s most powerful system boilers and has an ultra-quiet operation so you won’t be disturbed by off-putting noises.

The dimensions of this model are 850mm x 450mm x 360mm so this isn’t a compact boiler but still won’t take up a huge amount of room. 

The B2HB Vitodens 200-W 35kw comes complete with the stainless steel Inox-Radial heat exchanger that is designed for power and longevity. 

It has an environmentally responsible MatriX-Plus burner inside the boiler which helps distribute heat evenly and is cased in a durable shell with a sleek black, white and red design.

Which are the best oil-powered system boilers?

There are currently 49 oil-powered boilers on the UK market as of 2021 and the average price is £1,824.

Here, we have listed our top-rated oil-powered system boilers as ranked by the HomeSage boiler scoring system:

Which are the best electricity-powered system boilers?

If you opt for an electricity-powered system boiler, here is the HomeSage top 10 as scored in 2021. 

There are currently 19 models to choose from in the UK and the average price is £1,294.

Save up to 54% of your boiler installation with HomeSage

Fill in our online form to save up to 54% of the cost of the supply and the installation of your new system boiler. 

We get in touch with three or four local, trusted and Gas Safe regulated engineers with your query who will contact you directly with a free quote and relevant advice. 

Our service is completely free for you and it is no obligation even if you decide not to proceed. 

And if you’re looking for more critical information around what boiler is best for you, check out the HomeSage Advice Hub.