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Which are the most ethical and eco-friendly brands of gas and electric boiler?

Ratings for 15 brands of gas and electric boilers, with recommended buys. 

We also look at costs, grants, warranties, servicing, hydrogen boilers, energy efficiency and how to save energy. 

About Ethical Consumer

This is a shopping guide from Ethical Consumer, the UK's leading alternative consumer organisation. Since 1989 we've been researching and recording the social and environmental records of companies, and making the results available to you in a simple format.

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What to buy

What to look for when buying a gas boiler:

  • Look into heat pumps first as a lower carbon alternative (see our heat pumps guide). Also check out the grants section of this boiler guide for advice and support.

  • Can you choose the most efficient version? If you do need a boiler, a good installer can ensure you get the most efficient option.


Best Buys

No companies were eligible for Best Buy status because they all got a worst rating for the management of workers' rights in their supply chain.

Recommended buys

Most companies scored about the same, but those that were not marked down for tax conduct included:

Electric boilers: The smaller electric-only companies (Advance Appliances, EHC, Thermaflow, Elnur) plus Heatrae Sadia.

Advance Appliances, Electric Heating Company and Thermaflow are all small UK companies with turnovers under £10 million, specialising in electric heating products. Advance Appliances was the only one whose website stated that it manufactured all of its products in the UK.

Gas boilers: Baxi, Glow-worm, Main, Potterton, and Vaillant.

What not to buy

What to avoid when buying a gas boiler?

  • Is the company failing to report on its Scope 1-3 carbon emissions? See the section on carbon ratings for how the brands scored for this.

  • Does the company have subsidiaries in tax havens? See the tax conduct ratings section for which brands scored better here.

Companies to avoid

Worcester Bosch was one of the few companies to score worst for its tax conduct, and lobbying. It has also been involved in the VW emissions scandal.

  • Worcester Bosch

Score table

Updated live from our research database

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Brand Score(out of 100) Ratings Categories

Baxi gas boilers

Company Profile: Baxi Heating UK Ltd

Glow-worm gas boiler

Company Profile: Vaillant Group UK Limited

Heatrae Sadia electric boilers

Company Profile: Baxi Heating UK Ltd

Main gas boilers

Company Profile: Baxi Heating UK Ltd

Potterton gas boilers

Company Profile: Baxi Heating UK Ltd

Vaillant gas boilers

Company Profile: Vaillant Group UK Limited

Advance Appliances electric boilers


Electric Heating Company electric boilers


Thermaflow electric boilers

Company Profile: THERMAFLOW LTD

Elnur electric boilers

Company Profile: Elnur UK Limited

Ideal gas boilers

Company Profile: Ideal Boilers Limited

Keston gas boilers

Company Profile: Ideal Boilers Limited

Viessmann electric boilers

Company Profile: Viessmann Limited

Viessmann gas boilers

Company Profile: Viessmann Limited

Worcester Bosch gas boilers

Company Profile: Worcester Heat Systems

Our Analysis

Finding an ethical and eco-friendly boiler

From a climate perspective, heating is an urgent thing for consumers to address. It accounts for around 14% of the UK's greenhouse gas emissions if you count them territorially, or 9% including imports. And it has to be addressed at home, as that’s where the burning happens.

The UK is doing very badly at decarbonising heating. Houses in the UK are poorly insulated, and we are addicted to gas boilers.

Even if you’re not about to buy a boiler, this guide is still for you. If you find new ways to streamline your hot water requirements, adjust some boiler settings (and get your boiler serviced), you could cut costs and emissions right now.

Are there any environmentally-friendly boilers?

None of the brands in this guide receive our 'best buy' rating, and there's only four points between the top and bottom scoring brands. The finer details like price and warranties may help you differentiate between brands. We cover both topics in this guide.

If you are about to buy a boiler, we recommend that you don’t. A heat pump is much better for the climate if it’s possible for you. However, we realise that heat pumps are out of many people’s price range, so we are covering boilers again. This guide covers both gas and electric boilers.

There is a UK ban on fitting gas (and oil) boilers to new homes from 2025, with phase-outs for replacement boilers also expected, in order to wean ourselves off gas and cut carbon emissions.

Electric boilers v gas boilers

Electric boilers are not the best alternative for home heating. They are much more expensive to run than a gas boiler (because the price of electricity is higher than gas) and won’t currently save you carbon, although over their likely 15-year lifetime, the grid will hopefully decarbonise more and so that may change.

But even if it does, they would not be suitable for everyone as it would raise electricity demand too much on cold winter evenings when we all turn our heating up at once.

Electric heat pumps are several times more efficient at converting electricity to heat, and are the solution being proposed by the expert organisations. Our guide to heat pumps has more information.

Are electric boilers more energy efficient?

The ErP (Energy related Product) labelling of products for energy efficiency runs from G (likely rating for a non-condensing gas boiler which is under 70% efficient, pre-2005) to A (applies to all modern condensing gas boilers, which have the potential to be over 90% efficient.)

The label also lists the boiler's output (or 'size') in kW.

Although electric boilers are more efficient (up to 100%) than gas boilers at the point of use, confusingly, they have lower ErP ratings. This is for several reasons: the inefficiency and higher greenhouse gas emissions of UK electricity production at source, while it is still (about 40%) reliant on burning fossil fuels, and, the price of electricity.

Some campaigners argue that gas boilers ErP ratings should also be revised down for relying on fossil fuels, in order to better promote lower carbon products.

Looking ahead, about 40% of UK electricity production is already powered by renewables, and the National Grid is hoping wind and solar output will increase five-fold by 2030.

Can you make your boiler more efficient?

The efficiency percentage, which is not listed on the label, relates to how much of the energy used by the boiler actually heats the home, rather than just keeps the boiler running. However, a boiler will only reach its efficiency potential if it’s installed to do so, and many engineers have not been trained to do this.

Our energy savings tips further down in this guide suggest how you can change some settings yourself. A heating engineer could also adjust the ‘size’ of your boiler so that it is running on a lower ‘minimum output’ and condensing more efficiently.

How much does a boiler cost?

Boilers vary a lot in how much they cost to buy, install and run depending on a number of factors such as model, dimensions, efficiency, power, and controls.

All prices listed are excluding cost of installation and are indicative, according to what was found in January 2023.

Boiler brand and cost (2023)
Brand Purchase cost
Advance Appliances [E] £850 to £2,200
Baxi [G] £850 to £1,619
EHC [E] £1,065 to £2,618
Elnur [E] £940 to £2,357
Glow-worm [G] £550 to £1,789
Heatrae Sadia [E] £500 to £2,000
Ideal [G] £935 to £1,643
Keston [G] £1,140 to £2,610
Main [G] £515 to £830
Potterton [G] £498 to £2,140
Thermaflow [E] £2,250 to £4,175
Vaillant [G] £1,005 to £1,950
Viessmann [G] £928 to £1,898
Viessmann [E] £1,055 to £1,084
Worcester Bosch [G] £750 to £3,600

According to the Boilers Prices website, the average installation cost of having a new boiler fitted in the UK is around £1,500–£1,800. In terms of cost and complexity, gas boilers are generally more complicated to install compared to electric boilers.

Cost of running will depend on the size (its energy output in KW, rather than physical size) of the boiler, its efficiency rating, how many hours it’s in use per day and the number of radiators a person has in their home.

The only company that discussed the running costs of its products on its website was Thermaflow. Thermaflow’s website includes a useful summary of average annual running costs for its different electric boiler models, with costs ranging from around £1,000 to £2,000, depending on the volume and kW of the boiler, whether it was for 1-to-4-bedroom properties, and with the assumption that its use was for only two people.

Boiler replacement grants and other financial support

There are several government schemes and other grants which offer financial support for those needing to upgrade or replace a boiler.

The Boiler Upgrade Scheme is for homeowners in England and Wales (and Scotland also has a Home Energy Scotland Grant and Loan funding scheme), while others are more general home energy efficiency grants, and usually for low-income households, so you will need to check if you’re eligible to apply.

Boiler-specific grants

  • Boiler Upgrade Scheme. For three years from April 2022, the Boiler Upgrade Scheme allows households to apply for £5,000 government grants towards replacing a fossil fuel boiler with a heat pump or other renewable energy system.

Energy efficiency/heating grants

  • Energy Company Obligation (ECO). This government scheme is to support low-income and vulnerable households through boiler replacement or help with insulation costs. ECO4 came into force in July 2022 and will cover a four-year period until March 2026. You can also apply as a tenant if you’re privately renting (with your landlord’s permission) under certain conditions.
  • ECO+ or the Great British Insulation Scheme (GBIS) is designed to work alongside ECO and was introduced in 2023, for homes with an EPC rating of D or lower, EITHER in Council tax band A-D in England, or A-E in Scotland or Wales, OR on means-tested benefits. Look on your energy supplier's website or contact them for more details.
  • Green Deal loan. There are loans available to households wanting to make their properties more energy efficient through insulation, heating upgrades, and other measures. An assessment will need to be done for this.
  • Approaching your local authority for a grant. As can be seen with some of the grants below, the government are awarding a variety of grants to local authorities. So, it’s worth approaching your local council to make an enquiry about whether you might be eligible for financial support or what they can offer.
  • Home Upgrade Grant Scheme (England only). This is awarded to local authorities and will be available until March 2025, to support energy-efficient heating upgrades for households.
  • There are also competition-funded government grants available to local authorities, housing associations and registered charities that use social housing. For example, the Social Housing Decarbonisation Fund, which recently closed its latest round of bids. Its website has a contact email for future funding opportunities.

Some other useful places to look for financial support for a boiler upgrade include:

If you aren’t eligible for any schemes and can’t afford the upfront costs of a new boiler, Which? has advice on pay-monthly boilers and whether this might be the right choice for you.

Are second-hand boilers worth it?

As the advice on a boiler trade website puts it:

“Not many people upgrade their boiler when it is working perfectly, and this means finding a working combi boiler in good condition is a rarity. Also, how do you check your second-hand boiler is working properly before it is fitted?”

Newer boilers are also more energy efficient. So, although it might seem like an environment-saving action to buy a second-hand boiler, overall, that’s likely not to be the case once it’s installed and running.

Older used boilers may also not have easily available parts if they need repairing, as the manufacturer may have stopped producing parts for older models. It’s also unlikely that an older used boiler will still have its warranty.

A potential way to save on the cost of buying a new boiler is to approach a boiler or plumbing company and buy one of its ‘old’ display models in its shop.

Different boiler types and keeping bits for later

  • Combi boilers heat direct from mains water as needed, and won’t have an immersion heater or cylinder.
  • Heat-only (also known as conventional or regular) boilers are for larger homes and heavier usage, and have a hot (immersion) and cold water tank.
  • System boilers can be good where there is low pressure and have a hot (immersion) but not cold tank.

If you are disposing of a system with an immersion heater or cylinder, you may want to keep those parts, as they could work with a heat pump or solar panels you might get in the future.

Warranties for boilers

There is not much to separate the companies in this guide in terms of their Ethiscores, but when we looked at the warranties we found quite a large variation. So, it’s worth checking the terms and conditions, and how soon after acquiring a boiler you have to register it to receive cover (we found this was usually within 30 days).

Length of warranty ranged from one to twelve years, depending on who installed the boiler, if/when it was registered, and the model of boiler.

Electric boiler warranties tend to be shorter but they are less likely to have faults and it’s not as important to service them annually, compared to gas boilers.

The table below shows the warranty periods we found according to the brands’ terms and conditions if the boiler was registered.

Most brands had cover for both labour and parts, but some did not offer both for the duration of the warranty length (e.g. Electric Heating Company, Thermaflow). Some terms and conditions stated that a filter should be fitted, or an annual service should be carried out for the warranty to be valid.

A lot of the longer warranties were only available if an installer from the company selling the boiler fitted and registered it.

Boiler brand and warranty
Brand Warranty
Advance Appliances [E] 2 years
Baxi [G] 2 to 10 years
EHC [E] 5 years
Elnur [E] Up to 12 years
Glow-worm [G] Up to 10 years
Heatrae Sadia [E] n/a
Ideal [G] 2 to 12 years
Keston [G] Up to 7 years
Main [G] Up to 10 years
Potterton [G] 2 to 7 years
Thermaflow [E] 3 years
Vaillant [G] 2 to 10 years
Viessmann [G] 2 to 12 years
Viessmann [E] 2 to 12 years
Worcester Bosch [G] Online checker*

*Worcester Bosch did not offer a warranty but a guarantee, with a checker on its website.

Service your boiler

According to a Which? survey, around three in ten boilers that are serviced annually needed a repair in their first six years. This doubled to around six in ten boilers if the boiler was only serviced every two to five years.

They also found that paying for repairs only when needed was cheaper than paying through a boiler cover scheme. You might already have cover for boiler breakdown if you have home insurance, so check that too.

For servicing, Which? recommends a list of trusted traders, who are all Gas Safe-registered engineers, and it should cost about £86, as of January 2023. If you need reminders, you can get an app called Benchmark.

Are there any eco friendly boiler brands?

For this research we looked at what brands were doing about their carbon emissions and environmental reporting.

Discussions of reducing carbon impacts have improved overall since we last rated boilers but Vaillant, Bosch and BDR Thermea (Baxi, Heatrae Sadia, Main, Potterton) are still not calculating the carbon impact of their supply chains and the use of their products, which are known as Scope 3 emissions.

Groupe Atlantic (Ideal, Keston) is not even reporting the emissions of its own operations yet.

Viessmann was the only company with full reporting of its emissions and a credible reduction target. It talked about the investment it had made in powering its own operations with solar, heat pumps and green gases. However, it was marked down for owning a commercial airport and planes.

The electric boiler companies were generally proud of their focus on alternatives to gas boilers, and exploring lower-carbon tech. But none had any information on reducing their own impacts, either in terms of carbon or other environmental issues like water, waste, or materials – other than Elnur, which said it was producing its own energy to power 86% of its production processes.

In terms of other environmental issues, we found discussion of reducing water consumption (Vaillant, Bosch), waste (Groupe Atlantic, Viessmann, Bosch), and material usage (Viessmann, Bosch).

What are boiler companies doing about toxic substances in electronics?

Both gas and electric boilers have electrical components in them, so we scored companies for their policies on toxic substances used in electronic equipment.

All of the companies scored a worst for their lack of any publicly available policies on hazardous materials.

Radiator with three pairs of feet in socks resting on it

Change your boiler setting to save energy and money

In October 2022, the Money Saving Boiler Challenge was launched by Nesta, a UK charity that promotes innovation. They want at least one million households to change their combi boiler settings this winter to save energy.

It turns out that many boilers are installed to have a ‘flow temperature’ of 70-80°C but could be turned down to 60°C or even lower, using less gas and thereby saving emissions and money.

This is nothing to do with your thermostat and doesn’t mean your radiators won’t get as hot. It’ll just take a little longer than before, and the boiler will be able to condense more efficiently, recovering more heat as it’s designed to do. If your flow temperature was on 80 degrees to start with this could knock over £100 off your household’s annual energy bill and save you 170 kg of carbon emissions (which is about 1% of your total carbon footprint). And it only takes a few minutes to make the change.

Nesta also explains more ways that don’t cost anything to save gas at home, including lowering the settings on radiators, turning down the hot water temperature, and reducing the cylinder temperature safely if you don’t have a combi boiler – boilers with a hot water tank need to be kept over 60°C to avoid Legionnaires disease.

Energy saving tips from our readers

We asked our readers what they do to cut boiler costs, and carbon, and importantly how they avoid damp in a cooler home. Thank you everybody for a great response. We've included the main tips here and made them into an infographic (see below).

  • Consider solar hot water panels, or connecting to an immersion heater if you have solar PV.
  • Turn the water heater temperature down.
  • Turn the main thermostat down 1 degree.
  • Set room thermostats in unoccupied rooms lower.
  • Focus heating on the occupied rooms.
  • Shower, wash up, and do laundry less oftŒen.
  • Use the cold water tap unless it is too cold.
  • Wash laundry at 30°C.
  • Use the lowest temperature setting on dishwashers.
  • Use draught excluders for draughty doors.
  • Move about to warm up!
  • Wear tights or long-johns under trousers, and use a blanket when seated (or even an electric blanket).
  • Retro„fit your house with insulation and other features.

Plus, tips on how to reduce moisture indoors

  • Lower temperatures for laundry, dishwashers, and showers all produce less steam.
  • Check that outdoor gutters, pipes and drains are clear to prevent water entering the walls.
  • Dry laundry outside even in winter (unless raining!).
  • Use an extractor fan while cooking or showering.
  • Turn hobs down and cook with lids on.
  • Stop the kettle just as it boils and it’ll emit a lot less steam.
  • Invest in a compressor dehumidifier, and maybe a humidity monitor too.
  • Use a window vacuum cleaner or wipe away the condensation with a cloth every morning.
  • Wipe/squeegee the walls and ventilate the room straight after a shower.
  • Leave any trickle air vents on windows open all the time for fresh air circulation.
  • Open windows for 10 minutes after sleeping to let moisture escape.
  • Check behind furniture for moisture or mould and take action if necessary.
  • Clear clutter and furniture away from walls to allow for air flow and easier cleaning.

"I learnt that we feel more cold in damp humid air so if you can reduce the humidity you can turn your thermostat down without feeling a chill" Fran, Ethical Consumer worker

See more tips in our feature on home insulation and our feature on smart heating.

For more boiler related tips read the Energy Saving Trust's tips on boilers.

Infographic of drawing of open side of house with tips on saving heating. All tips are in the main text.
Image by Moonloft for ECRA

What are boiler companies doing about workers’ rights?

All of the companies we rated scored a worst for supply chain management and human rights.

None of the electric boiler companies had any publicly available information on their supply chain policies.

For gas boilers, none of the companies had policies on providing a living wage, and while all of the companies said they prohibited child labour, only BDR Thermea (Baxi, Main, Potterton, Heatrae Sadia) and Robert Bosch (Worcester Bosch) defined the age of a child.

Only BDR Thermea and Vaillant (including Glow-worm) had a complaints system where supply chain workers could make a complaint anonymously and free of charge in their chosen language.

Are any boiler companies avoiding tax?

Viessmann and Worcester Bosch scored worst for tax conduct, as both companies were found to have dubious company structures with high-risk company types registered in countries considered by Ethical Consumer to be tax havens.

Groupe Atlantic (Ideal, Keston) scored middle as its family tree was slightly less risky.

What can renters and landlords do?

Approximately 13 million people privately rent in the UK, one in five of the population. As a renter it might feel like you have no control over many aspects of your accommodation, including your boiler.

However there is increasing recognition that the way our homes are heated matters in terms of emissions, cost of living and energy poverty, and even as a renter there are still things you can do to try and upgrade (e.g. see the box above for the ECO4 scheme) or improve the efficiency of your boiler.

According to a recent survey from the National Residential Landlords Association in May 2022, four in five landlords agree that making their properties more energy efficient would provide tenants with support as prices rise, and two-thirds believe that they have a responsibility to help their tenants in this regard.

As a renter, joining a tenants union can link you to a community of people campaigning and putting pressure on councils and landlords for energy efficiency and a decent standard of rented homes. For example, Acorn has a National Renters Manifesto which includes “Private rented homes to address the climate emergency and help end fuel poverty.”

There is a high human cost to low-quality, energy-inefficient housing, with dire physical and mental health consequences for those unable to keep warm. Even at 10°C, which is the average temperature of an unheated home in the UK, this has health impacts on the brain, heart and lungs, and affects cognitive skills.

Write to your MP

The UK Government’s Heat and Buildings strategy, published in October 2021, outlined its goal for all new boiler installations to run on low-carbon technology by 2035, with natural gas boilers being phased out.

But the Climate Change Committee’s independent assessment of the strategy concluded that although a step in the right direction, funding and policy gaps remain, and many practical details were left unanswered.

There is more that the Government could be doing, and with much more urgency (like it’s a climate emergency, perhaps) if it’s going to reach its net zero target for households. Many measures also protect people from living in the cold.

If we are to reach the net zero carbon emissions target set by the UK Government, we will need to reduce the carbon emissions from heating our homes by 95% over the next 30 years. (Energy Saving Trust)

The UK Parliament website has a directory of MPs with contact email addresses. The Great Homes Upgrade campaign includes a toolkit, with resources such as templates for writing to MPs and local councillors. Our energy suppliers guide has a summary of five current energy-related campaigns.

Alternative to gas boilers

Hydrogen boilers are a diversion

In September 2022, the campaign organisation Global Witness released a report criticising several gas boiler companies for their misleading messaging around hydrogen boilers:

"Gas boiler companies are greenwashing their products with hydrogen- or hydrogen-blend ready labels, making them appear climate friendly."

All of the gas boiler manufacturers in this guide are members of the industry body EHI (European Heating Industry), which has lobbied for the EU to promote hydrogen-ready appliances, as well as phasing hydrogen into the gas system.

Bosch, Baxi (BDR Thermea) and Vaillant (Glow-worm, Vaillant) have all been saying “The only by-product of burning hydrogen gas is water”, while Viessmann said hydrogen is “emission-free”. However, when it is burned in air, rather than pure oxygen, it produces dangerous nitrogen oxides which exacerbate respiratory problems.

It’s true that burning hydrogen does not produce carbon emissions, but unfortunately, 96% of Europe’s hydrogen is currently produced by burning fossil fuels. There are also concerns about hydrogen leaks, as it reacts with other gases in the atmosphere, giving it a warming potential 33 times greater than carbon dioxide over a twenty-year period.

Hydrogen and cost

There are also big concerns around affordability. Global Witness referred to several studies which found heating with hydrogen boilers to cost more than heat pumps over their lifespan, even though heat pumps cost more to buy up front.

A separate review of 32 hydrogen studies, published in the peer-reviewed journal Joule, concluded that “hydrogen use for domestic heating is less economic, less efficient, more resource intensive” than several low- and no-carbon alternatives, and “associated with larger environmental impacts.”

A range of international and national bodies say that hydrogen fuel should be reserved for sectors where more efficient and cheaper technologies do not exist, i.e., not for home heating. Tempting people to buy ‘hydrogen-ready’ boilers, when no-one even knows if hydrogen will be used in this way, could distract people from the real alternatives and keep them on the grid.

The Global Witness report concludes that:

"Boiler manufacturers appear to be cynically and misleadingly marketing hydrogen-ready boilers, taking advantage of customers’ desire to take climate action, to allow themselves to continue to sell fossil gas boilers and avoid changes to their business models."

The Climate Change Committee – the statutory body that advises our government on decarbonisation – agrees that hydrogen is unlikely to be cheaper than heat pumps when you take everything into account. Its decarbonisation scenarios include only small amounts of hydrogen for heating, in combination with hybrid heat pumps.

What about biomass boilers?

Like hydrogen, the limited supply of biomass is generally agreed to be best used for other sectors where better low-carbon alternatives don’t already exist. For more information see the heating section of our Climate Gap report.

Additional research for the guide by Louisa Gould.

Company behind the brand

Robert Bosch (Worcester Bosch) is a company headquartered in Germany, established in 1886.

Starting off with its beginnings as a mechanical and electrical engineering workshop in Stuttgart, it’s now a multinational corporation specialising in technologies from power tools to automated driving.

Bosch technology was used in the Volkswagen’s diesel emissions scandal, which allowed the car manufacturer to cheat pollution testing. Bosch was prosecuted both in the US and Germany for its role in the scandal, with fines of $327.5 million and €90 million, respectively. The scandal also lost the company marks in our Pollution and Toxics and Irresponsible Marketing categories.

Want to know more?

If you want to find out detailed information about a company and more about its ethical rating, then click on a brand name in the Score table. 

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