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Last updated: 27th November, 2023


Back Boiler Replacement Costs, Guide and Tips

Back Boiler Replacement Costs, Guide and Tips

Key takeaways

  • Replacing a back boiler involves understanding costs, replacement options, and potential savings
  • Consulting registered engineers ensures compliance with legal requirements and safety
  • A back boiler replacement might require redecoration of the living space to accommodate the new heating system.

Should you replace that beaten up old back boiler and get with the times?

Back boilers have been a popular choice for homeowners in the UK since the 1960s, especially due to their space-saving design that fits behind a living room fireplace.

However, their popularity has diminished as more energy-efficient boilers hit the market.

Suppose you want to replace a back boiler in your home. In that case, it's essential to understand the costs, various replacement options, and any potential savings associated with upgrading to a modern heating system.

Before undertaking a back boiler replacement project, it is crucial to be aware of local regulations and the availability of registered engineers who are qualified to perform the job. They will ensure the safe removal of your existing boiler and compliance with all legal requirements.

Moreover, these professionals can help you determine the most suitable heating solution for your home, be it a combi-boiler or a regular boiler.

The conversion process requires careful planning, which might involve redecorating your living space after removing the back boiler.

What Is A Back Boiler?

Back boilers are quite an old type of boiler that fits behind an open fireplace rather than having its own cupboard or closed-off area.

Most of them were replaced in 2005 when the regulations around them changed, but there are still hundreds (if not thousands) in the UK that haven't been dealt with yet.

They may have been cheaper than normal boilers a few decades ago, but they are far more expensive to maintain nowadays.

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What is the Difference between back boilers and modern boilers?

The main difference between a back boiler and modern boilers is the way they work. They are 70% less efficient and generate a lot of useless heat, sometimes relying on warmth from the fireplace to warm the water inside.

Back boilers are also hard to repair since they are not being made any more, and fresh parts are nearly impossible to find.

It is rare to find a back boiler that isn't behind a fireplace, making it hard to change where they are installed.

This might also mean that back boilers take up a lot of space if you are not using the fire, which means that you can often save space by removing the entire fireplace along with the back boiler. This will cost slightly more, though.

Why did houses have back boilers?

Back boilers are essentially cheaper and smaller boiler, at least by the standards of when they were created.

They were easy to buy and could be hidden behind your fireplace, which kept them out of the way and made them suitable for smaller homes.

As mentioned earlier, they were extremely inefficient but could last much longer before breaking, thanks to their simple design.

The death of the back boiler

Unfortunately, since back boilers are almost impossible to repair easily, you will eventually have to replace or upgrade your existing boiler.

Even if it is still working, for now, the price and rarity of some key parts mean that it is probably just as expensive to repair as buying a new one, and there is no way to solve the efficiency problem without getting rid of the back boiler entirely.

Can you find back boilers in new homes?

If your house is new, it likely has no back boiler since its popularity dropped dramatically in the early 2000s.

Very few companies in the UK make them anymore, and it is tough to find brand-new back boilers anymore. Buying a new one is barely worth it anyway due to the massive efficiency problems they can have.

Should You Replace A Back Boiler With A Gas Boiler?

Back boilers only have one long-term upside: the small size. The lower price doesn't matter anymore since they're more expensive to run and will probably cost you more than a regular design. The long operational life doesn't mean much, considering it is not easy to repair them.

Accessing old back boilers can be a pain

The fact that they're kept out of the way also means that they can be hard to access without taking down parts of your fireplace, which can be annoying if something breaks or you want to make some small adjustments.

How big are back boilers?

The size of a back boiler doesn't matter as much, either. Modern boilers are smaller than those from the last two or three decades, so it's not hard to find a regular boiler that is the same size as (or even smaller than) your old back boiler.

This will only affect people with a minimal amount of space in their homes, but even if that's the case, you can find compact designs that will still offer higher efficiency.

New boilers are much more efficient

The higher efficiency makes a modern boiler far cheaper than a back boiler in the long run since you use less power to get the same results.

This can also help you get more consistent heat and provide better temperatures in general. Fixing a boiler isn't "cheap" in the usual sense, but it's still much less expensive than trying to repair a back boiler, and the money you save on your utility bills will make up for this.

Age of Boiler

Efficiency Percentage

Efficiency Rating (ErP)

0+ Years

90% +


10+ Years

85% +


15+ Years

80% +


20+ Years

70% +


25+ Years

60% +


The correlation between a boiler's age and efficiency is clear in the newer ERP systems. 

A new boiler will beat an old back boiler in a fight every day of the week!

Regardless of what your old back boiler model was, most people will choose a new combi boiler as a replacement since they are some of the most efficient and reliable models available to the general public.

These are also the most likely to work with your existing central heating system, so you generally won't need to swap out anything except the boiler itself.

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Back Boiler Replacement Costs

Different boiler designs will have their price differences, especially if you have to change more than just the boiler you use.

Back boiler replacements can range in cost from £2000 to £4000, depending on several factors, including the type and size of the back boiler, the age of your property, and whether or not there is any additional work required (such as replumbing)

Always make sure any engineer working on your back boiler is Gas Safe registered

If you're interested in a new combi boiler then we have a HUGE guide on finding the best combi boilers in 2022.

What's included in replacing a back boiler?

This cost of replacing a back boiler includes things like pipe capping, the installation of new pipes and upgrades to parts of your central heating.

If your boiler is going to be in a different part of the house, you'll have to pay for the pipe involved and the existing pipe that needs to be blocked up to stop leaks.

Upgrading to a system boiler VS a combi boiler

Some people prefer to go the "system upgrade" route, replacing the boiler but keeping the rest of the heating setup the same.

This can be a cheaper option since it involves minimal pipework, but it won't always be an option depending on the size and type of your new boiler.

On the other hand, some people want to redo the entire system to ensure it is completely fresh, reducing the chance of older parts breaking down or wearing out.

Costs aren't always set in stone, so you never know when your price might increase or decrease based on different options and situations.

Some houses might make setting up a new boiler far more expensive due to the thickness of their walls or the way the central heating system is set up. If you're looking into back boiler replacement, get a quote or estimate first.

Replacing a Back Boiler with a Combi Boiler

Replacing your boiler isn't too difficult, even if you do it yourself. As long as you understand the specifics of back boiler replacement, swapping them out doesn't take long.

Picking the right location for your new boiler

Sll boilers need a flue or some way to ventilate gases, ideally one that won't reduce its efficiency too much. Back boilers will vent these gases directly up the chimney, whereas a combi boiler can vent in horizontal and vertical directions.

This often means that you'll need to set things up differently, but it's sometimes possible to keep a similar flue and have it vent out of the chimney similarly.

Positioning a combi boiler

Many combi boilers can fit inside small spaces, like cupboards, so it is often possible to fit them in the same space as your older back boiler. They might also work in a kitchen cupboard, under-the-stairs area or behind an interior wall.

Relocation of you new boiler

If you want to move your boiler to a new area, you'll need to pay slightly more for the extra work, especially if there are no pipes there already.

Cost of relocation a back boiler conversion

This can cost anywhere from £300 to as high as £600 on average, or more if you have a larger house that needs more piping. You'll still usually be able to tie it into the existing central heating system, which can save some money on the installation.

Should You Keep Your Old Back Boiler?

There aren't many reasons to keep your back boiler unless you save money to install a new boiler.

As soon as you have the time and money to replace it, you should try and get it done since the higher efficiency will save more money. However, the fact that back boilers are long-lasting means that you don't necessarily have to swap them out immediately if you don't need to.

They'll break less often than a combi boiler, which can save some money if you're fortunate.

If your back boiler breaks to the point where you need to perform major repairs, you may as well get it replaced. It'll probably cost around the same amount in the long term, and it gives you a good opportunity to install a new boiler now that you've got a solid excuse.

Advantages of Back Boilers

One advantage of having a back boiler is that it doesn't take up much space in your room as it is located behind the fire.

They are also quite easy to install, and you can usually find someone who knows how to do it without too much trouble.

In addition, back boilers can be used to heat more than one room in your house as they circulate hot water through a wet central heating system.

Finally, if you have a gas-fired back boiler, you can use the heat from the fire to cook your food!

Disadvantages of Back Boilers

One disadvantage is that they can be quite expensive to run as you need to keep the fire going to generate heat.

In addition, if the fire goes out, you will need to wait for it to cool down before you can restart it, which can be quite annoying!

Finally, if you have a gas-fired back boiler, it is important to remember that they require regular servicing and maintenance to stay safe and efficient

Some back boilers can be cheaper to repair than others

Some back boiler models are cheaper to repair than others, depending on who made them and the parts they use, so it's not always a terrible idea to keep yours around for a while longer. However, it's still far more expensive overall, especially due to the massive drop in efficiency that'll increase your bill prices by quite a large amount.

Picking your new back boiler replacement

Always choose a new boiler you can rely on. Not all modern boilers are perfect, so if you're upgrading, you'll want to ensure you've gotten one that works well. A higher-quality boiler might cost slightly more, but you'll save plenty of money, which makes it a great trade-off.

Decommissioning your Back Boiler vs Removing it

When you replace your old back boiler, you must work out what to do with the old boiler and set up a new replacement combi boiler.

There are two main options: you can have your old boiler removed, clearing out the space and having it taken away, or you can simply have it decommissioned instead.

Making sure its safe

This means that it will be switched off and made safe, and then left in place exactly where it is, with no need to hire anyone to take it away.

So, what exactly is in this decision? Well, the first thing to bear in mind is cost. Having your back boiler decommissioned and left in place could save you up to £1000 from your full boiler replacement bill, which is potentially worthwhile!

Finance options for a back boiler replacement

If you plan on paying for your new boiler on finance rather than upfront, though, then this sort of saving might not have much of an impact on the size of your monthly repayments. If you are paying upfront, however, £1000 off your bill is worth considering!

It is worth noting that even if you opt to decommission your back boiler, engineers will still need to get behind your fireplace to access the boiler properly.

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Repairing the old back boiler location

That means you will probably still need to do some repair work afterwards, including things like replacing some of the surrounding flooring and potentially making repairs to your fire mantle or even replacing it completely.

Not every boiler can be safely decommissioned. Before deciding whether to decommission or remove your back boiler, you should call a gas-safe engineer to inspect it first.

If your gas-safe engineer declares your boiler safe to decommission without removing it, then the choice is entirely up to you. If your boiler is declared unsafe to decommission, the decision is out of your hands, and you must have the boiler obliterated.

Cost Implications and Saving Opportunities

Replacing a back boiler in the UK can be costly, but various grants and finance options can help homeowners save money. The back boiler replacement cost typically ranges from £3,500 to £5,500. However, the actual cost depends on several factors such as the type of new boiler, complexity of installation, and the heating engineer's fees.

Homeowners can significantly save on energy bills by upgrading to a more energy-efficient boiler. Modern boilers are designed to be more efficient than older back boilers, reducing carbon emissions and monthly heating bills.

Financial support is available to help ease the burden of back boiler replacement costs. Removal grants, for example, can provide 100% funding for back boiler removal and installation of a more efficient heating system. The amount of funding varies according to one's location, individual circumstances, and property.

Another option to explore is the Boiler Upgrade Scheme. This UK government initiative offers grants to cover part of the cost of replacing fossil fuel heating systems with a heat pump or biomass boiler. Eligibility for the scheme depends on various factors, including income, household circumstances, and geographical location.

To ensure getting the best deal on boiler replacements, homeowners should obtain comparison quotes from Gas Safe registered heating engineers in their area. This will enable them to consider various cost-effective options and make an informed decision.

In summary, while back boiler replacement costs may seem initially steep, the long-term savings on energy bills, coupled with available grants and finance options, present valuable opportunities for UK homeowners seeking a more energy-efficient and cost-effective heating solution.

Understanding Boiler Efficiency

When discussing back boiler replacement, it's crucial to comprehend the concept of boiler efficiency. Boiler efficiency plays a significant role in determining energy efficiency, which directly impacts energy consumption and costs. To gauge boiler efficiency, energy efficiency ratings are used. An understanding of these efficiency ratings can help homeowners make well-informed decisions about boiler replacements.

Boiler efficiency is a measure of how well a boiler converts fuel into heat. The higher the efficiency, the less fuel is required to generate the same amount of heat. Modern boilers tend to have higher efficiency ratings, translating to increased energy efficiency and reduced energy bills. In contrast, back boilers, which were popular in the 1960s and 1970s, are often plagued by poor energy efficiency, rendering them less desirable in today's eco-conscious world.

Energy efficiency ratings provide an easy-to-understand metric that allows homeowners to compare different boilers. The UK employs the ErP (Energy-related Products) directive, which assigns efficiency ratings ranging from A+++ to G. An A-rated boiler, for example, can achieve over 90% efficiency, while a G-rated boiler has an efficiency of 70% or lower.

Furthermore, it's essential to consider not only the boiler itself but also the entire central heating system when evaluating efficiency. An A-rated boiler, for instance, can achieve up to 200-400% efficiency when combined with modern electricity-run heat pumps. Thus, looking at the broader context of the heating system is key to optimising energy efficiency and minimising environmental impact.

To recap, boiler efficiency is a vital aspect to consider when exploring back boiler replacement options. Higher efficiency ratings lead to greater energy efficiency and cost savings, making it essential for homeowners to familiarise themselves with the various ratings when selecting a replacement. By understanding boiler efficiency and considering the complete heating system, one can make more informed decisions when it comes to replacing an old, less efficient back boiler with a modern, high-performing alternative.

Back Boiler Safety Risks

Sure, you could install a new boiler without getting rid of your old back boiler, but there are safety risks with that option that can create major problems.

If you have an old, unused back boiler in your house that has not been properly decommissioned, it can present a major safety hazard that should not be overlooked.

Safety first

An unused back boiler is still full of water, which can stagnate and create health hazards or can cause major issues with your heating system.

A large body of water such as this can build up pressure when the rest of your heating system is activated and starts to warm up. If this is not properly cut off from the rest of your heating system, the water in your old back boiler can build up a lot of pressure and cause leaks or even explosions.

Why Modern Gas Boilers Outshine Outdated Back Boilers

In the evolving world of home heating systems, the shift from outdated back boilers to modern gas boilers represents a significant leap in efficiency, technology, and environmental friendliness. Brands like Viessmann, Vaillant, Alpha, Ideal, and Worcester Bosch are leading this transformation, offering advanced solutions that far surpass the capabilities of traditional back boilers. Let’s delve into why modern gas boilers are the superior choice for contemporary homes.

Enhanced Efficiency and Energy Conservation

Modern gas boilers, such as the Viessmann Vitodens series, embody efficiency with innovative condensing technology. These models can achieve efficiency levels of over 98%, significantly reducing energy waste. In comparison, back boilers are typically non-condensing and much less efficient, often requiring more fuel for the same heat output, leading to higher energy consumption and costs.

Superior Heating Control and Comfort

Contemporary gas boilers offer unprecedented control over home heating. For example, the Worcester Bosch Greenstar i series integrates with smart thermostat systems, allowing precise temperature control and scheduling – a level of control unattainable with back boilers, which had limited flexibility and rudimentary controls.

Environmental Impact and Emissions

Modern gas boilers are designed with a lower carbon footprint in mind. Viessmann and Vaillant, for instance, focus on reducing emissions, with their latest models producing significantly fewer pollutants than boilers of the past. This shift is vital in global efforts to combat climate change and improve air quality, marking a significant advantage over older back boilers.

Safety and Reliability

Modern gas boilers are equipped with numerous safety features like automatic shut-off in case of malfunction, a stark contrast to the older back boilers. These features, coupled with regular maintenance and safety checks, which are more streamlined thanks to improved design and technology, make modern boilers far more reliable and safer.

Cost-Effectiveness Over Time

While initial investment in a modern gas boiler like the Worcester Bosch Greenstar 8000 Life or the Ideal Logic Max may be higher than maintaining an old back boiler, the long-term savings are substantial. Increased efficiency translates into lower energy bills, and their durability and lower maintenance requirements add to the financial benefits.

Comparative Efficiency Data and Technological Advancements

To understand the efficiency leap, consider that back boilers typically had efficiency ratings well below 80%, whereas modern boilers like the Alpha E-Tec range consistently exceed 90%. This jump in efficiency is largely due to advancements like modulating burners that adjust their output to match heating demand, dramatically reducing wasted energy.

Smart Home Integration and User Experience

Integration with smart home technology enhances user experience significantly. Modern boilers allow for remote control and system monitoring, providing homeowners with convenience and efficiency, a feature that was unimaginable with the more primitive back boilers.

Addressing Common Misconceptions

A common misconception is that modern gas boilers are more complex and difficult to operate than back boilers. In reality, advancements in user interface design have made modern boilers more user-friendly and easier to control.

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Frequently Asked Questions

What is the typical cost of a back boiler replacement in the UK?

The cost of back boiler replacement can vary depending on the specific model, location, and installation requirements. Typically, the costs can range from £1,500 to £3,500. This includes the price of the new boiler, as well as other expenses such as installation and materials. You must obtain multiple quotes from different installers to get the best possible deal for your specific circumstances.

Are back boilers still legal in the UK?

Although back boilers are not illegal, they have fallen out of favour due to their lower energy efficiency compared to modern boiler systems. However, it is worth noting that Building Regulations Part L1 in the UK requires any new boiler installations to be highly energy efficient. This means you are unlikely to have a new back boiler installed today, but existing ones are still permissible.

Which are the best back boiler replacement options in the UK?

There are several options to consider when replacing a back boiler. You could choose a regular or a combi boiler as an alternative. Your choice may depend on factors like your heating and hot water requirements and the existing infrastructure in your home, such as the pipework and the available space. It's essential to consult a professional installer who can assess your home and recommend the best option.

Is replacing a back boiler worth the investment?

Yes, replacing a back boiler with a more energy-efficient boiler can be a wise investment. Modern boiler systems can significantly save energy bills while reducing your carbon footprint. Additionally, old back boilers may have difficulty getting replacement parts, making maintenance and repairs more complicated and potentially costly. Upgrading your boiler can lead to greater reliability and increased home comfort.

Can a back boiler be replaced with a combi boiler?

Yes, a back boiler can be replaced with a combi boiler, which provides both central heating and instant hot water without needing a separate water cylinder. This change can result in improved energy efficiency, reduced energy bills, and increased living space, as combi boilers are more compact than back boilers. However, a professional installer should be consulted before taking this decision, as it may require some changes in your plumbing system.

Are any grants available for back boiler removal?

It's possible to receive financial assistance for back boiler removal and replacement in some cases. In the UK, specific grants, such as the government's ECO scheme, may support replacing inefficient boilers with more energy-efficient alternatives for eligible households. Contact your energy supplier or consult your local council for information on available grants and eligibility criteria.

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Article by
Stephen Day | Co-founder
Gas Safe registered and FGAS certified engineer with over 20 years experience in the heating and cooling industry.