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The Best Conventional Boilers in 2020

Deciding on a new boiler system can be an expensive business if you don’t do thorough research beforehand.

The system you currently have in your property can affect your choice as extra pipework and plumbing can add to the cost considerably. 

If you are upgrading your boiler from a much older system, your annual heating bills should come down with a newer and more efficient boiler system.

We know how complicated buying a new boiler can be so we’ve created this guide to give you an in-depth look at conventional boilers and we’ve ranked the top models available in the UK in 2020.

worcester bosch conventional boiler
Credit: Worcester Bosch

In this article, we discuss:

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What is a conventional boiler?

Conventional boilers, also known as regular boilers or traditional boilers, provide an excellent heat supply in a larger property that has increased hot water demands

They are best suited to properties which already have the piping system installed for a traditional heating and hot water system.

They require the most amount of space compared to combi boilers and system boilers.

They store cold water in a tank in the loft which is then piped down to the boiler below before being heated and retained in the hot water cylinder ready for use throughout your home.

These types of boilers are useful in older properties which have less advanced radiator systems which may not be able to handle the pressure produced by a system or combi boiler.

They also benefit those households needing consistent high water pressure

With a conventional boiler, you don’t lose pressure even if more than one person is using the hot water at any one time.

In fact, the only drawback is that you need to wait for the water to heat up again once you’ve emptied the tank.

Should your conventional boiler be powered by gas, electric, oil, or LPG?

In the UK there are four main options forfuelling your central heating system and availability often depends on the location of your property. 

If you are connected to the gas mains system, this is by far the cheapest and easiest option to go for as the cost is considerably lower than other fuels and you don’t need to worry about running out of fuel.

LPG – liquid paraffin gas – is the second most expensive way of heating your property and it relies on the delivery of gas from a supplier to your property’s storage tank. 

Heating oil works in a similar way, and although it is slightly cheaper than LPG, it is being phased out of use in the UK due to high costs and increased environmental concerns.

Both LPG and heating oil require regular delivery of fuel to your property which can be problematic if there is bad weather, road problems, or issues with your supplier. 

Electricity is an expensive way to heat your property and it costs the most per unit to fuel a central heating system though it doesn’t require as high of an output for your boiler.

FuelEmissions kgCO2 per kWhCost per kW unit (not on economy tariff)Hour’s running cost for a 27kw output boiler
Mains Gas0.2164p£1.08
Electricity0.51916p£4.32
LPG0.2417.6p£2.05
Heating oil0.2986p£1.62

Please note, although the above figures state the cost of running a 27kW boiler to be £4.32, a medium-sized home would require an electric boiler to have an output of around 11kW to provide the same amount of heat as the other methods.

Therefore, in reality the cost of heating the same size home by an electric boiler would more likely be approximately £1.76.

Due to the cheaper costs of running a gas fuelled boiler, most boiler installers would recommend choosing this method to power your central heating and hot water.

Upgrading your current boiler system allows you to save a substantial amount of money in heating bills.

This is because newer models are generally much more energy efficient and this should gradually offset the cost of replacing your old boiler.

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Choosing the best right sized conventional boiler for your home

Conventional boilers feature a variety of different power outputs and this is measured in kilowatts (kW). 

Choosing the right specification of output is important as there should be a balance between the size of the property you need to heat, your hot water requirements, and the power of the boiler itself. 

When you’ve got the correct level of output for your home, your boiler will be energy and cost efficient – choosing an output too low results in not enough power to heat the water, but too high means you could be paying more than you need to

The output of a boiler also tells you how much it will cost to run it and you work this out by multiplying the output by the cost of a unit of energy, for example a 33kW gas fuelled (0.04p per unit) boiler would cost £1.32.

Property sizeBathroomsRadiatorsBedroomsBoiler output rate
Small1Up to 121 or 2Up to 27kw
Medium1 or 212 to 182, 3, or 428-34kw
Large2 or more19 or more4 and above35kw+

The age of your property comes into play too because that often affects the standard of insulation you have and therefore the amount of power required to keep your property warm and cosy.

Let’s look at boilers for smaller properties.

If your home is pre-1900, it’s likely to have a poor level of insulation and a small property of 2 bedrooms would need an output of at least 18kW

A small property of the same size built post-2000 would only require an output of 13kW, in comparison.

With conventional boilers, you don’t need to worry about water flow rate because the water is not coming directly from the mains.

The best 10 gas-powered conventional boilers on the market right now

We think making your next boiler purchase should be easy and we want to help you be as informed as possible.

There are hundreds of conventional boilers to choose from in the UK and knowing which one will suit your property and budget can be a daunting task.

That’s why we’ve developed the HomeSage scoring system – a unique, online scoreboard for rating gas-powered conventional boilers by the following:

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

As you can see below, Worcester Bosch dominates our results due to their length of warranty, exceptional efficiency ratings and high level of excellent online reviews.

Check out our review of Worcester Bosch as a boiler manufacturer if you want more information on them!

Make and Model NameEfficiency RatingParts and Labour WarrantyOutput kWPrice fromTOTAL
Worcester Bosch Greenstar 12Ri Boiler92.00%6012£80091.79%
Worcester Bosch Greenstar 15Ri Boiler92.00%6015£82591.72%
Worcester Bosch Greenstar 18Ri Boiler92.00%6018£88091.59%
Worcester Bosch Greenstar 24Ri Boiler92.00%6024£93591.45%
Worcester Bosch Greenstar 21Ri Boiler92.00%6021£97591.36%
Worcester Bosch Greenstar 30Ri Boiler93.00%6030£1,06091.15%
Worcester Bosch Greenstar 27Ri  Boiler92.00%6027£1,09091.07%
Worcester Bosch Greenstar 8000 Life 30 Boiler94.00%6030£1,23090.73%
Worcester Bosch Greenstar 8000 Life 35 Boiler94.00%6035£1,51590.03%
Worcester Bosch Greenstar FS 30CDi Boiler92.00%6030£1,55589.93%
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The best gas-powered conventional boiler for a small property

For a small property of 1-2 bedrooms with 1 bathroom, you are likely to need a boiler with an output of up to 27kW.

There are currently 135 boilers available in this category and the average price is £961.

As you can see from our table, Worcester Bosch has the highest overall scores due to their energy efficiency ratings and lengthy warranties

Worcester Bosch Greenstar 12Ri Boiler (91.79%)

Make and ModelWorcester Bosch Greenstar 12Ri Boiler
TypeConventional
PowerGas
LocationInternal
Condensing?Condensing
Efficiency Rating92.00%
Band RatingA
LPG Compatible?Yes
Parts and Labour Warranty in months60
Heat Exchange Warranty in months60
Output kW12
MountingWall Mounted
Flow Rate in litres per secondN/A
Price from£800
Price to£830
ERP HeatA
ERP WaterN/A
TOTAL91.79%

The Worcester Bosch Greenstar 12Ri is a compact boiler that has been designed to fit within a standard kitchen cupboard measuring just 600mm x 390mm x 270mm.

It can be used as a replacement boiler within a property that already houses the pipework for a conventional boiler system.

This range from Worcester Bosch all have high energy efficiency ratings and this model is no different with an ‘A’ score at 92%. 

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Worcester Bosch Greenstar 15Ri Boiler (91.72%)

Make and ModelWorcester Bosch Greenstar 15Ri Boiler
TypeConventional
PowerGas
LocationInternal
Condensing?Condensing
Efficiency Rating92.00%
Band RatingA
LPG Compatible?Yes
Parts and Labour Warranty in months60
Heat Exchange Warranty in months60
Output kW15
MountingWall Mounted
Flow Rate in litres per secondN/A
Price from£825
Price to£860
ERP HeatA
ERP WaterN/A
TOTAL91.72%

A slightly more powerful model in the Greenstar range is the Worcester Bosch Greenstar 15Ri.

It has the same measurements of 600mm x 390mm x 270mm and is finished in a gloss white casing complete with a simple control panel.

All boilers in this range come with a 5-year warranty as standard.

This can be doubled to a 10 year warranty providing you install it via a Worcester Accredited engineer.

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Worcester Bosch Greenstar 18Ri Boiler (91.59%)

Make and ModelWorcester Bosch Greenstar 18Ri Boiler
TypeConventional
PowerGas
LocationInternal
Condensing?Condensing
Efficiency Rating92.00%
Band RatingA
LPG Compatible?Yes
Parts and Labour Warranty in months60
Heat Exchange Warranty in months60
Output kW18
MountingWall Mounted
Flow Rate in litres per secondN/A
Price from£880
Price to£915
ERP HeatA
ERP WaterN/A
TOTAL91.59%

For a smaller property requiring a little more power, consider the Greenstar 18Ri which also has a grade ‘A’ energy efficiency rating so you know your bills will be lower.

This boiler measures 600mm x 390mm x 270mm, comes with a standard 5-year warranty, and is front-access for easy installation and servicing.

This range of boilers all feature an easy-use control panel and it can be used alongside the Greenstore cylinder water storage system.

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Worcester Bosch Greenstar 24Ri Boiler (91.45%)

Make and ModelWorcester Bosch Greenstar 24Ri Boiler
TypeConventional
PowerGas
LocationInternal
Condensing?Condensing
Efficiency Rating92.00%
Band RatingA
LPG Compatible?Yes
Parts and Labour Warranty in months60
Heat Exchange Warranty in months60
Output kW24
MountingWall Mounted
Flow Rate in litres per secondN/A
Price from£935
Price to£975
ERP HeatA
ERP WaterN/A
TOTAL91.45%

Small homes with greater hot water requirements need look no further than the Worcester Bosch Greenstar 24Ri. 

It is compact in size at 600mm x 390mm x 270mm but large on power with a 24kW output. 

You can opt for a 10-year warranty with this product provided it is installed by a Worcester Bosch accredited Gas Safe engineer, otherwise it is a standard 5-year warranty out the box.

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Worcester Bosch Greenstar 21Ri Boiler (91.36%)

Make and ModelWorcester Bosch Greenstar 21Ri Boiler
TypeConventional
PowerGas
LocationInternal
Condensing?Condensing
Efficiency Rating92.00%
Band RatingA
LPG Compatible?Yes
Parts and Labour Warranty in months60
Heat Exchange Warranty in months60
Output kW21
MountingWall Mounted
Flow Rate in litres per secondN/A
Price from£975
Price to£1,015
ERP HeatA
ERP WaterN/A
TOTAL91.36%

Coming in last for the small property options is the Worcester Bosch Greenstar 21Ri but only due to its fractionally higher price tag.

This boiler measures 600mm x 390mm x 270mm so it’s identical in size to the other Greenstars in this range and it can easily be installed behind a kitchen cupboard door.

This boiler can be used in conjunction with the Greenskies range of solar panels for increased energy efficiency and improved environmental sustainability

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Best choice of conventional boilers for a medium sized property

Semi-detached homes or larger terraced properties with 2-4 bedrooms and 1-2 bathrooms should consider a boiler with an output of between 28-34kW.

As of June 2020, there are 15 conventional boilers in this category and the average price is £1,211.

Worcester Bosch Greenstar 30Ri Boiler (91.15%)

Make and ModelWorcester Bosch Greenstar 30Ri Boiler
TypeConventional
PowerGas
LocationInternal
Condensing?Condensing
Efficiency Rating93.00%
Band RatingA
LPG Compatible?Yes
Parts and Labour Warranty in months60
Heat Exchange Warranty in months60
Output kW30
MountingWall Mounted
Flow Rate in litres per secondN/A
Price from£1,060
Price to£1,100
ERP HeatA
ERP WaterN/A
TOTAL91.15%


One of the highest output models available in the Worcester Bosch Greenstar range is the 30Ri boiler which comes complete with a grade ‘A’ energy efficiency rating. 

The boiler’s dimensions are 600mm x 290mm x 270mm so certainly classed as a compact boiler.

Providing you install this boiler using a Worcester Bosch accredited engineer and follow the terms and conditions, you have a 10-year warranty should anything go wrong.

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Worcester Bosch Greenstar 8000 Life 30kw Boiler (90.73%)

Make and ModelWorcester Bosch Greenstar 8000 Life 30 Boiler
TypeConventional
PowerGas
LocationInternal
Condensing?Condensing
Efficiency Rating94.00%
Band RatingA
LPG Compatible?Yes
Parts and Labour Warranty in months60
Heat Exchange Warranty in months60
Output kW30
MountingWall Mounted
Flow Rate in litres per secondN/A
Price from£1,230
Price to£1,280
ERP HeatA
ERP WaterN/A
TOTAL90.73%


The Greenstar life range of boilers are smart, modern, and include many technological features that improve the ease and comfort of heating your home. 

The measurements of this model are 780mm x 440mm x 365mm which makes it slightly on the larger size.

It is available in a gloss white finish featuring an attractive digital circular control screen.

It automatically refills your system to the optimum level which removes the need for you to manually check it. 

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Worcester Bosch Greenstar FS 30CDi Boiler (89.93%)

Make and ModelWorcester Bosch Greenstar FS 30CDi Boiler
TypeConventional
PowerGas
LocationInternal
Condensing?Condensing
Efficiency Rating92.00%
Band RatingA
LPG Compatible?Yes
Parts and Labour Warranty in months60
Heat Exchange Warranty in months60
Output kW30
MountingFloor Standing
Flow Rate in litres per secondN/A
Price from£1,555
Price to£1,620
ERP HeatA
ERP WaterN/A
TOTAL89.93%


This floor-standing boiler measures 850mm x 400mm x 600mm and has been designed to neatly slot underneath a standard kitchen counter. 

The high-quality internal components are housed in a traditional durable white casing.

It benefits from a ‘roll in’ boiler so you won’t damage your flooring during installation and maintenance. 

The warranty for this boiler is up to 8-years providing you follow the terms and conditions provided regarding installation and annual servicing

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Baxi 430 Heat 30kw Boiler (88.44%)

Make and ModelBaxi 430 Heat 30 Boiler
TypeConventional
PowerGas
LocationInternal
Condensing?Condensing
Efficiency Rating89.10%
Band RatingB
LPG Compatible?No
Parts and Labour Warranty in months60
Heat Exchange Warranty in months60
Output kW30
MountingWall Mounted
Flow Rate in litres per secondN/A
Price from£905
Price to£945
ERP HeatA
ERP WaterN/A
TOTAL88.44%


With a slightly lower energy efficiency rating than the equivalent output Worcester Bosch boiler, the Baxi 430 Heat 30kw has a SEDBUK energy grading of ‘B’.

It measures 625mm x 370mm x 270mm, it is a wall-hung unit and it has a remarkably low weight of 19.5kg.

This boiler comes complete with a standard 5-year warranty.

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Baxi 230 Heat 30kw Boiler (86.94%)

Make and ModelBaxi 230 Heat 30 Boiler
TypeConventional
PowerGas
LocationInternal
Condensing?Condensing
Efficiency Rating89.10%
Band RatingB
LPG Compatible?No
Parts and Labour Warranty in months36
Heat Exchange Warranty in months36
Output kW30
MountingWall Mounted
Flow Rate in litres per secondN/A
Price from£835
Price to£865
ERP HeatA
ERP WaterN/A
TOTAL86.94%


This is one of the newest conventional boilers available from UK manufacturer Baxi.

It measures 625mm x 370mm x 270mm so it is compact enough to be installed within a kitchen unit to save on space in your property. 

This boiler has front and side access for servicing and installation and comes with a 3-year warranty as standard. 

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Conventional boilers to consider for a larger property

If you’re choosing a conventional boiler for a semi-detached or detached home with 4+ bedrooms and 3+ bathrooms, you will most likely require a boiler with an output of 35kW+ to make sure your hot water supply doesn’t fall short. 

Currently in this category there are 18 boilers to consider with an average price of £1,445 each. 

Worcester Bosch Greenstar 8000 Life 35kw Boiler (90.03%)

Make and ModelWorcester Bosch Greenstar 8000 Life 35 Boiler
TypeConventional
PowerGas
LocationInternal
Condensing?Condensing
Efficiency Rating94.00%
Band RatingA
LPG Compatible?Yes
Parts and Labour Warranty in months60
Heat Exchange Warranty in months60
Output kW35
MountingWall Mounted
Flow Rate in litres per secondN/A
Price from£1,515
Price to£1,575
ERP HeatA
ERP WaterN/A
TOTAL90.03%

Featuring the same slick aesthetic as the Greenstar 8000 Life 30kW model, this slightly more powerful boiler has been designed with style and substance in mind. 

The Worcester Bosch Greenstar 8000 Life 35kw measures 824.95mm x 440mm x 364.6mm so is on the larger size.

But, with its white gloss finish and unique port-hole style control panel, you won’t want to hide it away. 

This boiler can be linked to your smartphone for effortless heating and hot water control on the go. 

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Vaillant ecoTEC plus 435 35kw Boiler (83.72%)

Make and ModelVaillant ecoTEC plus 435 35 Boiler
TypeConventional
PowerGas
LocationInternal
Condensing?Condensing
Efficiency Rating89.20%
Band RatingB
LPG Compatible?Yes
Parts and Labour Warranty in months60
Heat Exchange Warranty in months60
Output kW35
MountingWall Mounted
Flow Rate in litres per secondN/A
Price from£1,470
Price to£1,530
ERP HeatA
ERP WaterN/A
TOTAL83.72%

This boiler is hand-built in the Derbyshire Vaillant factory and comes complete with a 5-year guarantee for your peace of mind.

This can be extended to 7 years if installed by a Vaillant Advance technician. 

The dimensions of this boiler are 600mm x 375mm x 340mm and it is lightweight for easy installation.

The ecoTEC plus 435 35kw benefits from a two-stage frost protection system so you don’t need to worry about pipework freezing over, even if your boiler is installed in the garage. 

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Vaillant EcoFIT Pure 35kw Boiler (81.70%)

Make and ModelVaillant ecoFIT Pure 35 Boiler
TypeConventional
PowerGas
LocationInternal
Condensing?Condensing
Efficiency Rating89.70%
Band RatingB
LPG Compatible?No
Parts and Labour Warranty in months24
Heat Exchange Warranty in months24
Output kW35
MountingWall Mounted
Flow Rate in litres per secondN/A
Price from£1,275
Price to£1,325
ERP HeatA
ERP WaterN/A
TOTAL81.70%

The Vaillant EcoFIT Pure 35kw boiler comes with a slightly shorter warranty time of 2-years as standard, although you can increase this to 7 or 10 years upon installation by a certified Vaillant engineer.

The dimensions of this model are 600mm x 375mm x 295mm for a compact fit in your home.

This boiler benefits from automatic heat control, and it can reduce its output to 20% of its maximum heat if required, meaning you save extra money on your energy bill. 

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Viessmann WB1B Vitodens 100-W 35kw Boiler (78.76%)

Make and ModelViessmann WB1B Vitodens 100-W 35 Boiler
TypeConventional
PowerGas
LocationInternal
Condensing?Condensing
Efficiency Rating88.70%
Band RatingB
LPG Compatible?Yes
Parts and Labour Warranty in months60
Heat Exchange Warranty in months120
Output kW35
MountingWall Mounted
Flow Rate in litres per secondN/A
Price from£1,175
Price to£1,225
ERP HeatA
ERP WaterN/A
TOTAL78.76%

Many Viessmann boilers have a separate warranty for their internal Inox-Radial heat exchanger and the WB1B Vitodens 100-W 35kw is no different.

The boiler has a 5-year warranty as standard, however the internal heat exchanger as a 10-year warranty should it develop a fault.

This boiler measures 600mm x 375mm x 285mm and benefits from a back-lit LED display screen and 2 easy-use control knobs

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Ideal Mexico HE MEX 36kw Boiler (72.92%)

Make and ModelIdeal Mexico HE MEX 36 Boiler
TypeConventional
PowerGas
LocationInternal
Condensing?Condensing
Efficiency Rating89.00%
Band RatingB
LPG Compatible?No
Parts and Labour Warranty in months24
Heat Exchange Warranty in months24
Output kW37
MountingFloor Standing
Flow Rate in litres per secondN/A
Price from£2,715
Price to£2,825
ERP HeatA
ERP WaterN/A
TOTAL72.92%

The first Ideal boiler to feature in the HomeSage results is the Mexico HE MEX 36kw.

This boiler comes with a 2-year warranty, it is a floor-standing unit and it’s often used as a replacement boiler for traditional heating systems.

It measures 850mm x 450mm x 530mm so it’s slightly deeper than most boilers however it should still fit under a kitchen unit to conserve space. 

It weighs 68kg and has a user-friendly status display so you can check your boiler performance at a glance. 

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Which are the best oil-powered conventional boilers?

Should you opt for an oil-powered conventional boiler, Worcester Bosch offers the highest rating models according to the HomeSage results. 

Worcester Bosch is the only manufacturer to score over 80% on their total score and the closest competition is a Warmflow boiler with an overall total score of 77.54%.

There are currently 144 models on the market and the average price is £1,788.

Make and Model NameEfficiency RatingParts and Labour WarrantyOutput kWPrice fromTOTAL
Worcester Bosch Greenstar Danesmoor 12/18 Boiler90.00%2418£1,40082.81%
Worcester Bosch Greenstar Danesmoor Utility 12/18 Boiler90.00%2418£1,41582.77%
Worcester Bosch Greenstar Danesmoor Utility 18/25 Boiler90.00%2425£1,52082.51%
Worcester Bosch Greenstar Danesmoor 18/25 Boiler90.00%2425£1,66582.16%
Worcester Bosch Greenstar Danesmoor 18/25 Boiler90.00%2425£1,84081.73%
Worcester Bosch Greenstar Danesmoor 12/18 Boiler90.00%2418£1,85081.70%
Worcester Bosch Greenstar Danesmoor Utility 25/32 Boiler91.00%2432£1,91081.56%
Worcester Bosch Greenstar Danesmoor 25/32 Boiler90.00%2432£2,06081.19%
Worcester Bosch Greenstar Utility 32/50 Boiler90.00%2450£2,16580.93%
Worcester Bosch Greenstar Danesmoor 25/32 Boiler91.00%2432£2,19080.87%
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Save up to 54% of your boiler installation with HomeSage

You can save up to 54% of the cost of the supply and the installation of your new conventional boiler by filling in your details on our online form. 

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

Our service is completely free for you and it is no obligation, regardless of your final decision!

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Andy

Andy is one of the HomeSage founders and an occasional content contributor. His love for boilers is only just outweighed by his love for football.