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Combi Boiler Installation: Process and Price Guide in 2025
- A new combi boiler installation ensures energy efficiency, cost savings, space-saving design, and on-demand hot water.
- Fitting a new boiler (connecting the boiler to the existing pipework and system) can be done in one day, usually between 4 and 6 hours.
- The average cost for installing a new combi boiler is around £3,800. Replacing an old combi with a new one can cost between £1,600 - £6,000, and converting from a different type of boiler can cost from £1,600 - £6,500.
Combi boilers dominate the UK market for a reason. Their high efficiency (92% and above) translates to lower energy bills and a gentler environmental impact. A new combi boiler installation simply involves the removal of your existing boiler and fitting the new combi boiler, and it might also involve replacing the pipework. Installing a new combi boiler could save you up to £490 annually!
This article explores the factors affecting combi boiler installation costs, including boiler type and home size. For a precise new boiler cost tailored to your home, consider getting quotes from qualified engineers. However, finding a trustworthy expert can stretch for days if done alone.
Thankfully, GreenMatch can connect you with up to 3 vetted professionals for a hassle-free comparison and installation process. Our service is completely free and it only takes 30 seconds to get started.
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Combi boiler installation process
How do you install a new combi boiler? Below, we’ve outlined everything involved in a simple combi boiler installation.
- Old boiler removal: The old boiler is disconnected from the gas supply and removed alongside any fixtures holding the boiler in place. An existing hot water cylinder or cold water tank may also need to be removed.
- System flush: Chemicals are left in the heating system to break down any debris which can then be flushed out. Your installer might also recommend a power flush depending on the amount of debris build-up.
- Laying new pipework: The combi boiler must be installed with gas pipework that is at least 22mm in diameter to withstand high volumes of gas on demand. Therefore, 15mm pipes will need to be upgraded.
- Fitting the new boiler: Installing in a new location will require additional parts and labour costs. Fitting your new boiler is straightforward as long as the installer can easily access the area.
- Additional upgrades: There are several options to help maintain your new boiler. These include a magnetic filter to prevent debris build-up, a new boiler flue, and heating controls.
- Registering your new boiler: Your new boiler will need to be registered with the manufacturer to ensure your warranty is valid.
A combi boiler installation could take anywhere from 4 hours up to 3 days. More complicated installations will take the longest.
These might involve having a combi boiler fitted in a new location in the home or switching from a system or conventional (regular) boiler type. The process can also be complicated if the boiler is located in a difficult-to-access area, such as a loft.
Combi boiler installation diagram
A combi boiler installation involves connecting the new boiler to the main water network, gas supply, and central heating system pipework, via which hot water can be delivered to your radiators and hot water outlets. Take a closer look below:
How long does it take to fit a boiler?
| Combi-to-combi boiler swap | 4-6 hours |
| New boiler replacement | Up to 3 days |
Fitting a new boiler (connecting the boiler to the existing pipework and system) can be done in one day, usually between 4 and 6 hours.
A straightforward like-for-like combi boiler replacement in the same location typically takes 4-6 hours. This involves replacing the existing boiler without extensive adjustments.
However, if you are installing a new type of boiler, the timeframe may extend up to 3 days or more. This is because removing the old boiler and adjustments to pipework are necessary. Also, additional tasks may include adding or removing the external hot water tank.
It's crucial to note that relocating the boiler can significantly impact both time and cost. If, for instance, the installation site is difficult to access, the process might exceed the 3-day timeframe.
You can search for installers and get a time estimate yourself, but how time-consuming and stressful would that be? Would you know if the installer you spent hours looking for was certified and had all the necessary expertise?
Thankfully, we can do the legwork for you. Fill out our 30-second form to obtain up to 3 no-obligation quotes from our extensive network of vetted boiler installers. Simply click the button below to receive free quotes to compare.
- Quotes from local engineers
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Installation cost of a combi boiler
Fitting a combi boiler typically costs between £1,600 - £6,000, or £3,800 on average. More complex installations usually involve switching to a new boiler type or moving the boiler to a new location in the home.
For these types of replacements, the pipework will need to be adjusted, and additional units will need to be removed. This could cost up to £4,000 or more.
Combi to combi boiler replacement costs
This type of ‘like-for-like’ swap will likely cost an average of £1,600 - £6,000, comparatively less than other boiler replacements.
The combi boiler replacement process is relatively straightforward and typically takes about 4-6 hours, as it does not involve significant changes to the existing infrastructure.
| Combi-combi boiler replacement | Average price range |
|---|---|
| New combi boiler | £600 - £4,000 |
| Installation costs | £1,000 - £2,000 |
*Price estimates include all fuel types (gas, LPG, oil, & electric)
System to combi installation costs
Replacing a system boiler with a combi takes additional time and labour to adjust the pipework and remove the hot water cylinder.
On average, this will cost around £1,500–£5,600 and requires 2-3 days of work.
| System-combi boiler replacement | Average price range |
|---|---|
| New combi boiler | £600 - £3,000 |
| Installation costs | £1,000-£2,600 |
*Price estimates include all fuel types (gas, LPG, oil, & electric)
Conventional to combi installation costs
A conventional-to-combi boiler replacement takes the most time since the hot water cylinder and additional cold water tank must also be removed. Together, these costs will reach around £4,500 to have a combi boiler fitted.
Given the higher price range for this type of boiler replacement, it might serve you well to instead consider a new conventional boiler to keep installation costs down.
| Conventional-combi boiler replacement | Average price range |
|---|---|
| New combi boiler | £600 - £3,500 |
| Installation costs | £1,000-£3,500 |
*Price estimates include all fuel types (gas, LPG, oil, & electric)
These numbers are just estimates and can differ from your home's final combi boiler installation price. Consult an experienced local boiler engineer to get the most tailored advice.
When should you get a new combi boiler installed?
There are several indicators that it might be time to replace your existing boiler:
- Age: Boilers typically last between 10 and 15 years. If your boiler is approaching this age, it may be time to consider a replacement boiler.
- Frequent breakdowns: If your boiler requires frequent repairs or has recurring issues, it may be more cost-effective to replace it rather than continue with repairs.
- Rising energy bills: Older boilers are less efficient. If you notice a significant increase in your energy bills without a corresponding increase in usage, it could be a sign that your boiler is no longer operating efficiently.
- Inconsistent heating: If your radiators take a long time to heat up or you experience an inconsistent hot water supply, it may indicate that your boiler is struggling to meet your home's demands.
- Unusual noises or smells: Strange noises or smells coming from your boiler can indicate serious issues that may require replacement.
Call the Gas Emergency Services: 0800 111 999 in England, Scotland and Wales or 0800 002 001 in Northern Ireland.
Remember carbon monoxide does not smell. You must install a carbon monoxide detector if you have any gas appliances in your home.
If your carbon monoxide alarm sounds, evacuate the property immediately and call the emergency gas line.
Make sure your boiler gets regular maintenance and timely replacements so that your new heating system remains safe, efficient and reliable.
Advantages of a new combi boiler installation
Combi boilers have become a popular choice for many homeowners due to their numerous benefits:
- High efficiency: Combi boilers have an efficiency rating of 90-94%, leading to significant savings on energy bills.
- Compact size: These boilers don't require separate hot water cylinders or cold water storage tanks, making them ideal for smaller homes or properties with limited space. They can often be installed in kitchen cupboards or other small spaces.
- Instant hot water: Combi boilers provide hot water on demand directly from the mains, eliminating the need for a hot water storage tank. This means you get instant hot water whenever you need it.
- Easy installation: Combi boiler installation is generally easier and quicker, with fewer components required compared to other systems.
- Cost-effective: Due to their efficiency and the reduced need for additional components, combi boilers can be more cost-effective both in terms of installation and ongoing maintenance.
- Space-saving: The absence of bulky water tanks frees up space in your home, which can be used for other purposes.
Which combi boiler should you install?
Selecting the right combi boiler for your home takes some careful consideration of several key factors. Below, we outline these factors and highlight some models from the best combi boiler brands in the UK to help you make an informed decision.
Boiler size
The size of a combi boiler is measured in kilowatts (kW) and determines how much heating and hot water it can provide. Choosing the right size depends on the number of bathrooms, radiators, and water usage in your home:
- 18-27kW: Suitable for small homes or apartments with 1-2 bedrooms and up to 10 radiators.
- 28-34kW: Ideal for medium-sized homes with 2-3 bedrooms and 10-15 radiators.
- 35kW+: Best for large homes with 4+ bedrooms, multiple bathrooms, and over 15 radiators.
If your home has high heating demands or multiple bathrooms in use at the same time, a system boiler may be a better alternative as combi boilers can struggle to provide sufficient hot water in such cases.
Efficiency
Boiler efficiency directly impacts energy consumption and running costs. The higher the efficiency rating, the less fuel is wasted. Most combi boilers have 92-94% efficiency, which means they convert almost all of the fuel into useful heat.
When it comes to energy efficiency, the Viessmann Vitodens 200-W stands out with an impressive efficiency rating of up to 98%.
Warranty
A good warranty provides peace of mind and protection against costly repairs. Warranty lengths vary by manufacturer, but a 10-12 year warranty can be considered as a good choice. Most companies will also offer extended coverage.
The ATAG iC combi boiler range offers an industry-leading standard 12-year warranty, with an option to extend up to 18 years, making it one of the best warranty options on the market.
Additional considerations
A combi boiler installation can come with some additional parts and labour costs, depending on the condition of your existing heating system. Some of these costs may include:
- A magnetic filter to help prevent debris build-up: £100 – £300
- Boiler flue replacement for releasing waste gases outside the home: £300 – £600
- Heating controls to improve comfort levels and energy saving: £150 – £300
Get new combi boiler installation quotes
Every home has unique specifications that help decide the final new combi boiler and installation costs. Therefore, consulting a professional combi boiler installer is the best way to learn the true costs, how long the job will take, and any additional components to consider.
Comparing quotes from multiple installers is a cost-effective way to find the best combi boiler deals and the cheapest rates. However, such research can take days or weeks if done alone.
GreenMatch can eliminate this extra effort by directly connecting you with up to 3 heating engineers from our network of trusted installers. All of our installers are Gas Safe or OFTEC registered. Simply click the button below to be taken to our 30-second form.
- Quotes from local engineers
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- Save up to £975
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- Combi Boiler Installation: Process and Price Guide in 2025
- Combi boiler installation process
- How long does it take to fit a boiler?
- Installation cost of a combi boiler
- When should you get a new combi boiler installed?
- Advantages of a new combi boiler installation
- Which combi boiler should you install?
- Get new combi boiler installation quotes
- FAQ
- Quotes from local engineers
- Payment by finance available
- Save up to £975