Back Boiler Replacement

Save money on your heating bills by replacing your back boiler.
Read about back boiler replacement and what's included.

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Back Boiler Replacement

Witten by Bernard Morgan (Engineer) & Adam Apperley (Marketing). Published: November 9, 2023. Updated: May 9, 2024

In this guide we’ll look quickly at what a back boiler is and how they work. Then we’ll discuss why you should replace it with a combi boiler.

Key points:

  • Back boilers are old an inefficient
  • Replacing one will cost between £3,000 and £4,500
  • You will save £100s on your energy bills each year

What is a back boiler?

Back boiler replacement guide | Boilerhut

Back boilers are a type of conventional (or regular) boiler. They are vented systems that take a cold water feed from a tank in your loft. They provide hot water to a hot water tank for taps and showers and heat your radiators.

They were first installed in the 1960s, and although they are inefficient, back boilers are very robust, often lasting 30-50 years.

How does a back boiler work?

A gas fire heats water for your radiators and hot water tank the same way that modern boilers do. The front fireplace doesn’t need to be lit for the back boiler to work in the background. A back boiler relies on a pilot light rather than an electrical spark like modern boilers.

For a detailed breakdown of how back boilers work read our guide.

Why replace your back boiler?

A back boiler is generally about 50-70% efficient. This means half the money you’re spending on heating is wasted. They are also very reliable, meaning you might be wasting money for a long time.

Combined with the pilot light, inefficient heat transfer and the old hot water tank, you are spending money when you don’t need to. Installation of new back boilers is now illegal due to their inefficiency. Here are some reasons why you should replace your back boiler:

  1. Less energy efficient than modern boilers. You will be wasting £100s a year on your heating bills.
  2. High carbon emissions.
  3. Repair is becoming increasingly complex, with no parts being available.
  4. Potential safety issues.
  5. Expensive to run wasting 50p in every £1 spent.

Back boiler replacement costs

The costs will depend on two things: the cost of decommissioning (removal or not) and the cost of the new boiler and pipework.

A combi boiler replacing a back boiler will cost between £3,000 and £4,500 depending on your requirements.

If you leave the back boiler in place and decommission it, the price will be lower. Full removal of the back boiler will push the price up and it is a more complicated job.

Below is an approximation for a back boiler to combi boiler swap:

Combi Boiler Model Cost – Boiler Only Cost – Installed
Viessmann Vitodens 050-W From £1,060 From £3,300
Viessmann Vitodens 100-W From £1,427 From £3,600
Viessmann Vitodens 111-W From £2,254 From £4,200
Worcester Greenstar 4000 From £1,541 From £3,800
Alpha E-Tec NX From £810 From £3,000

What to replace your back boiler with

When it’s time to replace your old back boiler, you’ll have a few choices: a combi boiler, a system boiler, or a regular boiler. While all three options are viable, our recommendation is almost always a combi boiler.

The main reason a combi boiler is the best option for a back boiler swap is the size of the home. Back boilers tended to be installed in 2-3 bedroom homes with 1 or 2 bathrooms. A combi boiler can nicely replace the back boiler in terms of power. It can also fit into the airing cupboard where the hot water cylinder was installed.

From a cost and complexity perspective, we strongly believe that replacing a back boiler with a system or regular boiler wouldn’t be a wise choice. Both options would necessitate a new hot water cylinder, significantly increasing the cost to a range of £4,000 to £8,000. In contrast, a combi boiler offers a more cost-effective solution.

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Does the back boiler need to be removed?

No. When it comes to replacing a back boiler, there are two options: remove or leave. In either case, it’s crucial that the back boiler is drained down and made safe, ensuring your peace of mind and the safety of your home.

Leaving the back boiler in place

The most common option is to leave the back boiler in place. This means it remains where it is, but is safely hidden away. Once the back boiler is made safe, the new pipework and boiler can be installed, ensuring a seamless transition.

Removing the back boiler

A qualified heating engineer will expertly remove the back boiler, front fire, and cylinder (if necessary). They will also remove or reuse pipes where possible. Gas, water, and electricity will be cut off, allowing for the safe removal of the old boiler.

Removing a back boiler is a messy job. It will also leave a hole where it used to be. A heating engineer will leave the space as tidy as possible.

Most heating engineers can perform a plumber’s finish. This will include adding battons, fixing plywood, and skimming with plaster. Once the plaster has dried, you will be able to paint.

Boilerhut case study

This is a back boiler to combi boiler conversion project.

One of Boilerhut’s heating engineers removed a back boiler and hot water cylinder. The back boiler is decommissioned and removed before the installation of a new combi boiler.

The installation includes new copper pipework and a new combi boiler. In this home, the boiler was placed in the attic as there was no room in the kitchen. The back boiler was replaced with a Viessmann Vitodens 050-W 28kW combi boiler.

Boilerhut case study of a back boiler replacement in 2021.

Baxi Bermuda back boiler

Baxi Bermuda Back Boiler - Back Boiler Replacement | BoilerhutBaxi back boilers used to be the backbone of many homes and continue to be reliable…but very inefficient compared to new boilers.

The BAXI Bermuda back boiler was so common it’s likely that if you have a back boiler this was the model.

Identifying your Baxi back boiler is simple. Open the flap at the bottom and locate the label or model number. No matter how reliable these back boilers are, they will eventually break down. Unfortunately, parts are pretty rare, and even if they weren’t, we’d recommend upgrading. This would be to a modern condensing boiler.

The Baxi Bermuda BBU HE was a condensing back boiler. However, it has been discontinued by Baxi. The main reason they didn’t do well is because they required a Baxi electric fire which meant replacing the gas fireplace.

Need to replace your back boiler?

If you need a new or replacement boiler or are looking at having a central heating system installed, get an online quote (it takes less than 1 minute), and you’ll get an instant price. But why choose Boilerhut:

  • Next day boiler installation.
  • Instant, no-obligation quote in less than 1 minute.
  • Boiler finance options available for new boilers and central heating installation.
  • 10 to 12-year warranty on boilers.
  • ‘Excellent’ 5* customer satisfaction on Boilerhut’s Trustpilot.
  • Fixed prices. No hidden extras.
  • Get up to three quotes for different-tier boilers.

Frequently asked questions

There are a number of different types of heating systems available, so it is important to choose one that is right for your needs. You should consider the size of your home, the number of people who live there, and your budget. You should consult with Boilerhut to get advice on the best type of heating system for your property. Get an online quote now >

Yes, we offer a warranty on all of our boiler replacements through the manufacturer. The warranty period varies depending on the type of boiler you choose. In order to keep the warranty valid you will need to service the boiler correctly and yearly.

We can offer 12 year warranties on some Viessmann boilers as we’re a Viessmann Premium Partner.

Yes, we can help you to finance your boiler replacement. Grab an online quote now and we’ll call you back to get all the final details – there’s no need for us to visit the property for a survey. Just ask about finance options or read more about them on our finance page >

Back boilers are far less complicated than modern boilers and have a life expectancy of 20 years or more. However, this means they’re highly inefficient and the older they get the higher the risks become. Older pipes and metal work can degrade over time. Flues and air intakes can become blocked causing dangerous gases to backup into the home.

If you have a back boiler, it may be working “well” but we would suggest at the very least getting it checked out to ensure your safety. However, the main reason to replace it will be that you will save money on your energy bills.

Back boilers are very costly to run, wasting 30% or more of the energy you pay for. New condensing boilers in the UK have to be a minimum of 90%+ efficient. We work with Viessmann as their boilers are super efficient and long-lasting. Their Vitodens 200-W is 98% efficient.

  • Low efficiency.
  • High running costs.
  • No instant hot water.
  • Potential for carbon monoxide build-up.
  • Required ventilation – meaning outside air cools the air the fire is heating.

No. Not compared with new condensing boilers. Some back boilers are estimated to be around 50% efficient which means 50% of the cost is wasted in heat up the chimney or flue.

Most back boiler are gas powered. However, there are also solid fuel back boilers that run on coal or wood. These tend to be even more inefficient than gas back boilers.

A back boiler circulator is a pump that circulates hot water around your system.

If you know you have a back boiler, then yes, it is most likely behind your fireplace. This could be gas or solid fuel powered. Even if decommissioned a back boiler may have been left in place to save costs during a back boiler to combi conversion.

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