If you live in an older home, you’ve probably heard of a boiler. These were popular heating systems that were installed behind fireplaces. They provided hot water and heating by burning gas or solid fuels. However, today backboilers are outdated, inefficient and even unsafe.
So if you still have one, you might be thinking about replacing it. But how much does it cost to replace a reheat boiler? The answer is not easy. Several factors affect the overall price, such as the new system you choose, the condition of your current system, and the size of your home.
In this guide we explain everything for you. You will learn what back boilers are, why they need to be replaced and the overall costs involved. We’ll also help you understand your options and what to expect during the process.
What is a back boiler?
A back boiler is a small boiler unit that sits behind a fireplace or stove. It heats water for radiators and taps. It became popular in the United Kingdom in the 1960s and 70s.
These boilers worked well at the time. However, over the years they have proven to be less energy efficient and more difficult to maintain than modern systems. Many reheat boilers are no longer supported or cannot be repaired for safety reasons.
Why should you replace a back boiler?
Here are the main reasons why people choose a boiler replacement grant:
1. Low efficiency
Back boilers typically have an energy efficiency of around 70%. In comparison, modern condensing boilers can achieve over 90%. This means that with a reheat boiler you are likely to waste energy and pay higher bills.
2. Security risks
Some old baking kettles, particularly the Baxi Bermuda models, proved to be dangerous if not properly maintained. Cracks and leaks can lead to carbon monoxide leaks. Many models are now banned or are no longer manufactured.
3. Fix problems
Spare parts are difficult to find. Qualified engineers who can work on reheat boilers are also rare. Most professionals recommend removing them completely.
4. Legal and compliance issues
Current building regulations make installing a new after-heat boiler almost impossible. If you plan to sell or rent your home, you may need to replace the old system to comply with standards.
What options are there for rear boiler replacement?
When replacing a reheat boiler, you essentially have three options. Each one impacts the overall cost.
1. Combi boiler
A combi boiler (combination boiler) is the most popular option. It heats water on demand and does not require a hot water cylinder or storage tank. It is compact and ideal for smaller homes.
Advantages:
- Saves space
- Lower operating costs
- Energy efficient
Disadvantages:
- Possibly problems with high hot water demand
2. System boiler
A system boiler requires a separate hot water tank, but not a cold water tank. It works well in larger homes where hot water is needed in multiple places at once.
Advantages:
- Good for homes with multiple bathrooms
- Works well with solar panels
Disadvantages:
- Requires more space than a combi boiler
3. Normal or pure boiler
This most closely matches your back boiler setup. It uses a hot water tank and a cold water tank. If your home already has this system, it may be cheaper to upgrade this way.
Advantages:
- Keeps the same layout
- Ideal for older properties
Disadvantages:
- Less efficient than modern combi boilers
Rear boiler replacement cost
Let’s get to the big question: How much does it cost to replace a reheat boiler? Here you will find a breakdown of all costs involved.
1. Cost per boiler unit
- Combi boiler: £1,500 – £2,500
- System boiler: £1,600 – £2,700
- Regular boiler: £1,400 – £2,500
The price depends on the brand, size and energy efficiency class. Popular brands like Worcester Bosch, Vaillant and Ideal may cost more but offer longer warranties.
2. Installation costs
The installation effort often makes up the largest part of the total cost. Replacing a rear boiler is not an easy change. It requires:
- Removing the old back boiler
- Changing the pipes
- Install the new boiler somewhere else
- Seal or remove the chimney
- Repair and redecorate walls
Expect to pay between £2,000 and £3,000 for installation alone.
3. Additional parts and labor
You may also need additional materials such as:
- New chimney or smoke plume kit: £100 – £300
- New controls or smart thermostat: £100 – £250
- Magnetic filter: £100 – £150
- Power flushing the system: £300 – £600
Labor and time requirements also increase if your home is difficult to access, the plumbing is outdated, or if you move the boiler far from its original location.
Estimated total cost
Let’s put it all together.
| option | Boiler + installation + extras |
| Combi boiler | £3,500 – £5,000 |
| System boiler | £3,800 – £5,500 |
| Normal boiler | £3,400 – £5,000 |
These are guidelines for a standard 2 to 3 bedroom house in the UK. The final cost will depend on your property, location and boiler choice.
How long does it take to replace a back boiler?
Most rear boiler replacement jobs take 3 to 5 days. Here’s why:
- Day 1-2: Removal of old boiler and chimney work
- Day 3-4: Installing the new boiler and connecting new pipes
- Day 5: Tests, power flushing and final checks
If there are complications, it may take longer. However, a trained engineer can provide a clearer time estimate after inspecting your home.
Can I get help with the costs?
Yes! Several UK programs can help with the cost of replacing rear boilers:
1. Boiler Upgrade Program (BUS)
This helps homeowners switch to low-carbon heating. You could get up to £7,500 by replacing your boiler with a heat pump or renewable system.
2. ECO4 program
If you receive certain benefits, you may be eligible for free boiler replacement under the Energy Company Obligation program. In some cases this also includes the removal of back boilers.
3. Financing options
Many boiler manufacturers offer payment plans or 0% financing. This can help you spread the cost over 2 to 10 years.
What happens to the fireplace?
Since there are back boilers behind the fireplaces, you have to deal with the space they leave behind. You have several options:
- Completely shut off and plaster over
- Install an electric fire for decoration
- Add a closet or wall
Some homeowners even choose to install a wood stove in the room. Just make sure your installer properly seals the chimney to avoid drafts or safety issues.
Do I need a building permit?
In most cases you do not need a building permit to replace a back boiler. However:
- If your home is listed or in a nature reserve, check with your local authority
- For any gas work you will need a Gas Safe registered technician
- Building regulations apply to all boiler installations
Always ensure that your installer provides a certificate of compliance with building regulations upon completion of the work.
Frequently asked questions about boiler replacement
Q: Can I repair my old baking kettle instead of replacing it?
A: In most cases, no. Spare parts are rare and many back boilers can no longer be repaired.
Q: Is it cheaper to keep my hot water tank?
A: Sometimes. If you choose a system or regular boiler, you can use your current storage. But if it’s old, it might still be best to replace it.
Q: Which boiler is best for replacing a rear boiler?
A: For smaller homes, a combination boiler is ideal. For larger homes, a system boiler may be better.
Final thoughts
Replacing a baking kettle is a big job. But it is often necessary for safety, efficiency and comfort. Although it can cost between £3,500 and £5,500, the long-term savings on your energy bills make it worth it.
Choosing the right system depends on the size, layout and hot water needs of your home. A registered installer can help you choose the best option and complete the process safely.
Regardless of whether you choose a combination, system or regular boiler, be sure to compare prices, ask about warranties and check whether you are eligible for Eco4 scheme funding.
Replacing a boiler may seem costly at first, but it’s a smart move for a warmer, safer and more efficient home.
