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Last Updated on November 13, 2023

Back Boiler Replacement

Back boiler replacement isn’t a hot topic, because even though they’re old and inefficient, they are extremely reliable and still a common fixture in homes across the UK.

At Boilerhut, we specialise in back boiler gas fire replacement. This is the replacement of a back boiler with a much more efficient modern condensing boiler such as a combi boiler.

We recognise that back boilers are very reliable but they are also very inefficient. On average, for every £1000 you spend on gas you are wasting about £450. By investing in a new A-rated combi boiler, you will save money and help reduce your carbon footprint.

What is a back boiler?

Back boilers are a type of conventional boiler that were designed to be installed into the recess of an open fireplace hearth and hidden behind a gas fire.

As they are conventional boilers, a back boiler system requires a back boiler unit (BBU), plus a separate cold water tank and hot water cylinder to be installed elsewhere in your home, to provide heating and hot water. The cold water tanks will usually be found in the loft, whilst the hot water cylinder will usually be found in an airing cupboard.

First installed in the 1960s with the launch of the Baxi Bermuda, and still being installed into homes as recently as 2005, back boilers were seen to be a great choice due to their compact dimensions and ability to be hidden away.

However, changes to UK building regulations in 2005 meant that new boilers installed into UK properties need to be condensing, and as the majority of back boilers are not condensing, the installation of them stopped. Whilst back boilers haven’t been installed into properties for 16 years, there are still many of these in homes across the UK.

If you have a back boiler in your home, you have a boiler that is much more inefficient than modern condensing boilers available today.

On average, back boilers operate at 50% efficiency or less with degradation over time. This means that for every £1.00 you are spending on gas, at least 50p of it is being wasted.

This is not great for your wallet or the environment.

Can you still buy back boilers?

No, all of the major back boiler manufacturers including Baxi, Rayburn, and Glow Worm have stopped producing back boilers which means that new models are no longer available for sale. There was an attempt to launch condensing back boilers after 2005 with the availability of back boilers such as the Baxi Bermuda BBU HE, however, these were largely unsuccessful due to the flue alone costing £1500 on average.

It is possible to buy second-hand back boilers. However, this can be a risk as they will not come with a warranty, there can be safety concerns, and they also will not meet current building regulations. At Boilerhut, we don’t recommend the purchase of second-hand back boilers for these reasons.

You should always consult a qualified heating engineer before making a decision on installing any kind of new heating system.

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Back boiler replacement options

The majority of heating engineers will recommend the replacement of a back boiler, even if it can be repaired. There are two main reasons for this – cost-effectiveness and safety.

Cost-effectiveness comes down to the inefficiencies of back boilers compared to the 90%+ efficiencies offered by modern A-rated condensing boilers that equal great cost savings. In addition, the scarce availability of parts for these boilers can also drive up the cost of repairing a back boiler.

A major issue with back boilers is debris coming down the chimney and blocking the flue which will cause carbon monoxide to leak into the property, which in the worst-case scenario and can be lethal. If you have a back boiler, or any boiler or fuel burning heating or cooking device we would recommend having a carbon monoxide alarm in the same room to ensure your safety.

A back boiler also requires permanent ventilation to the outside which allows for cold air to get back into the property, reducing the overall efficiency of the heating system.

What’s next…

Due to the above, we recommend replacing a back boiler with another type of boiler…even if it is still working.

We primarily recommend replacing a back boiler with a combi boiler. This will allow you to free up space in your property that the cold water tanks and the hot water cylinder will currently be taking up. However, if a combi boiler is not suitable for your home and the needs of your household, a modern condensing sealed or conventional boiler can be installed instead.

The most popular replacement option is back boiler to combi boiler, with the combi boiler installed where the old hot water cylinder would have been sited usually in an airing cupboard.

One further consideration is when you convert to a combi, you are increasing the pressure on the heating circuit. If the existing pipework and/or radiators are in poor condition, there is also a possibility of leaks and problems, so you may require new pipes and/or radiators.

We are happy to discuss this with you at length before any work is started. We have converted many back boilers to combi or full-system boilers in the last few years.

What to do with the current back boiler?

There are two options for the current back boiler. These options are:

The removal of the entire back boiler system

This will involve draining down the heating and hot water circuits, removing the back boiler and fire and disconnecting the pipes attaching it to your hot water cylinder and cold water tank. We then remove all of the components of the back boiler from the fireplace that it is installed into. Removing a back boiler can be quite a large-scale and messy job. This will leave a hole in your wall that will need to be blocked up and made good (something Boilerhut and most heating engineers will not b eable to help with).

Decommissioning of the back boiler and fire but leaving it in place

Rather than completely removing the back boiler appliance, we almost always recommend decommissioning them, but leaving it in place.

The Health and Safety Executive has issued clear guidance for homeowners looking into replacing back boilers. They recommended that a redundant back boiler left in situ must be in a condition that means that an unsafe level of pressure cannot build up in the unit. Bearing this in mind, we offer a service that involves us decommissioning, draining, capping off the gas and any electrical connections to the back boiler, and ensuring that it is left completely safe.

Once this is done to the back boiler and fire, we will then be able to install the pipework for the new boiler and install the new boiler in a new location in your home.

A recent back boiler to combi boiler conversion project

Below, you will be able to watch a video that shows one of our installers decommissioning and removing a 30+ year old Baxi Bermuda back boiler unit, and replacing it with a Viessmann 050-W 29kW combi boiler.

Link to back boiler to combi boiler conversion video

How much does a back boiler replacement cost?

How much it costs to replace a back boiler can vary from property to property. It is dependent on factors including how difficult it is to access it, which usually comes down to how much clearance there is at the side to enable a tradesman to access it. The type of boiler you want to replace it with will also have an impact on the cost.

The main factor that impacts the cost is whether you wish to decommission and leave in situ or completely remove.

There are other factors to take into consideration, which we list below.

At Boilerhut, we find that customers request a combi boiler most often to replace a back boiler. We are able to offer advice and a free quote for those looking for a back boiler replacement.

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How much does a back boiler to combi conversion cost?

he average back boiler to combi boiler installation cost is between £3,000 to £4,500 inc. VAT.

Replacing a back boiler with a combi boiler requires additional work than other types of boiler replacement, this is due to the nature of this type of boiler. The back boiler will need to be decommissioned. This can either be removed, or it can be left in place but disconnected from the gas mains – the choice is yours and is something that we will discuss with you ahead of the installation.

What’s included in a back boiler to combi boiler installation?

  • Modern condensing combi boiler
  • A vertical flue (most back boiler to combi boiler installations will use a vertical flu rather than a horizontal flue)
  • Microbubble deaerator (if needed)
  • Magnetic filter (if needed)
  • Limescale filter (if needed)
  • A Boiler Plus compliant programmable thermostat or an internet-enabled learning thermostat
  • North-facing weather compensation
  • All necessary pipework including a gas upgrade

In addition to the above items, we also provide the following when undertaking a back boiler to combi boiler installation at Boilerhut:

  • Chemical flush and inhibitor
  • Up to 10-year parts and labour warranty
  • Commissioning of the boiler and benchmarking
  • Building Regulation notification with certification including landlord certificates
  • Handover and induction on the boiler and controls

Does a back boiler replacement make sense for you?

The simple answer is yes.

Back boilers were once popular because they were the most energy and space-efficient technology available. 40 years ago, combi boilers were much larger than they are today. For housebuilders, they were easy to have installed. Homeowners appreciated the simple technology that made them reliable and easy to fix if they went wrong.

Environmental regulations have improved since the 1970s, and condensing boilers are now compulsory for all boiler installations.

The government has recently launched ambitious new carbon zero targets for the UK. It is likely there will be continued efforts to encourage households with heating systems with below minimum operating efficiency – like back boilers – to switch over the coming years.

If you are looking into a back boiler replacement you may be concerned about the cost. However, it is important to factor in the savings you will make by replacing a back boiler.

The main reason we recommend replacing a back boiler is that there are so many cost-effective and high-performance boilers on the market that can reduce your energy bills, particularly if you currently have a gas stove to power your back boiler. Switching to a combi boiler can save you over £450 each year on a £1000 gas bill, which would be common if you are a medium to high user.

It is worth noting that back boilers have a reputation for reliability, they are relatively simple technology and can often be kept going for decades with regular servicing. However, it is increasingly difficult to find replacement parts for back boilers because it has been such a long time since they were manufactured.

If your home has a gas back boiler, upgrading to a combi boiler can reduce your household heating bills and save you a lot of hassle if it breaks down.

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Save up to £590 PER YEAR on your heating bills.
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