Combi Boiler Installation: Costs & Guide (2025)
- Installing a combi boiler leads to annual energy savings of up to £490 and lower energy bills.
- The upfront cost of installing a combi boiler instead of a regular or system one, including installation, falls in the region of £1,140-£7,200, costing on average around £4, 200.
- A combi-for-combi installation can be performed within a day, usually taking between 4-6 hours.
Combi boilers are the most popular choice in the UK. They don’t take up much space, and there’s no need for any additional tanks or cylinders. This can mean that a new combi boiler installation is generally faster and less disruptive than other boiler types.
So, if you’re looking to maximise the space in your home and join the millions of other homeowners in the UK who enjoy all the benefits of a new combi boiler, here’s everything you need to know about the installation process and costs.
However, if you've already made up your mind on what type of boiler you want but would like to find out how much a new boiler costs, you will need an installer you can trust. Instead of wasting hours of your precious time researching local installers, let us put you in touch with up to 3 Gas Safe registered combi boiler installers quickly and easily.
Fill in our 30-second form, and sit back and relax while trusted professionals vetted by us get back to you with tailor-made boiler quotes. You can then compare figures to find the installer that best suits your needs and secure the best deal for your home. Click below to get started now!
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How does a combi boiler installation work?
Unlike traditional or system boilers, combi boilers don’t require a separate water tank or a cylinder, which makes it a perfect fit for smaller homes and flats. The installation process involves connecting the boiler to the gas supply, water pipes, and waste outlet.
Here’s how the combi boiler installation works in more detail.
- Mounting the boiler: The heating engineer will use a plywood panel to secure the boiler. Once secured, the boiler is hung on metal brackets.
- Connecting gas supply: Next, the gas pipe is connected to the boiler for further water heating through a gas valve.
- Cold and hot water inlet connection: In a typical setup, the cold and hot water outlets are connected to the boiler using 15mm pipings.
- Waste pipe installation: The waste (condensate) is usually acidic. The waste pipe is installed internally to prevent this corrosive liquid from freezing in cold weather and damaging the system.
- Electrical connections: New electrical cables are connected to the boiler to power sensors, pumps, and control circuits.
- Flue installation: Two 10-cm-diameter holes are drilled through the exterior wall - one for exhaust and the other for air intake.
After the installation is done, the heating engineer checks the gas, water, and electricity connections to ensure there are no leaks. They also adjust the system pressure and temperature settings to optimal levels.
Make sure your boiler is installed by a Gas Safe registered engineer (or OFTEC registered engineer in the case of oil boilers) who can complete the Benchmark checklist. This is a legal requirement for working on gas appliances in the UK.
How long does a combi boiler installation take?
The installation of a combi boiler typically takes about 1-2 days, depending on several factors. Expect a straightforward combi-for-combi replacement to be done within 4-6 hours. However, switching from a conventional or system boiler requires significant pipework changes and can take up to 2 days.
When planning the installation time, factor in the boiler’s location, whether new radiators will be fitted and the complexity of the overall heating system.
New combi boiler installation costs
Combi boiler prices range from as little as £540 up to £4,250 with an additional £1,500-£3,500 installation fee. The prices depend on the brand, output, and fuel type (combi oil boilers tend to be more expensive than combi gas boilers).
The tables below give some averages for combi boiler costs for the most common fuel types.
| New combi boiler installation costs | ||
| Fuel type | Boiler price range | Average inc. cost |
|---|---|---|
| Gas | £540-£3,500 | £1,500-£3,500 |
| Oil | £1,300-£4,250 | £3,200-£3,400 |
| Electricity | £1,000-£3,150 | £1,600-£3,500 |
However, installing a brand new boiler isn’t always the situation. Some heating projects require a boiler replacement due to a system upgrade. Therefore, homeowners face different price ranges, which largely depend on the scope of work needed for the replacement.
Replacing a combi with a combi
The costs for this kind of boiler swap can range anywhere from £1,140 to £5,200 for a typical 3-bedroom home. Your expenses will be higher or lower depending on the size of your boiler and whether you’re planning on moving a boiler within your home.
| Combi-combi replacement | Average price range |
|---|---|
| New combi boiler | £540-£3,700 |
| Installation costs | £600-£1,500 |
If you are considering changing your boiler, the easiest way to go about it is to replace a combi boiler with a new combi boiler. Because it requires no or minimal changes to the pipework and because no additional components like water cylinders or storage tanks need to be removed, the new combi boiler installation can occur in about 1-2 days.
Replacing a system boiler with a combi
Changing from a system boiler to a combi boiler costs around £1,540 – £6,300. However, prices may be higher because the installation process is longer than that of swapping an old combi boiler with a new combi boiler.
| System-combi replacement | Average price range |
|---|---|
| New combi boiler | £560-£3,700 |
| Installation costs | £1,000-£2,600 |
Fitting a combi boiler to replace a system boiler involves removing the hot water cylinder and potentially adjusting the pipework. This can take about 2 days or more to complete, so you can end up spending more on labour costs.
Changing from a regular boiler to a combi
If you're switching from a regular boiler, you can expect to pay somewhere between £1,540 and £7,200. This kind of replacement is the most costly, as it requires the removal of a feed and expansion tank in the attic as well as a hot water storage cylinder.
| Regular-combi replacement | Average price range |
|---|---|
| New combi boiler | £600-£3,700 |
| Installation costs | £1,000-£3,500 |
The combi boiler gets its water supply directly from the mains, so more pipework will be required. As a result, having a combi boiler fitted to replace a regular boiler can take 2.5 days or more, depending on the complexity of the installation.
The surefire way to find a boiler that suits your requirements is to consult several heating engineers in your area. However, finding an installer you can trust can stretch for days and weeks if done alone.
By filling in our short form, you can receive up to 3 quotes for a brand-new boiler from trustworthy professionals near you. Then, just compare quotes to choose a reliable installer to work with and to find the best deal for your new combi boiler.
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Why should you get a new combi boiler fitted?
Upgrading an old boiler to a new combi unit can drastically improve your home’s efficiency and comfort. A modern combi boiler comes with some solid advantages.
- Improved energy efficiency: While gas boilers have an efficiency rating of around 93%, most electric combi boilers can boast one as high as 99%-100%.
- Space-saving design: When compared to conventional boilers, combi units are more compact and can even fit into a kitchen cupboard as they don’t need separate hot water tanks.
- On-demand hot water: Combi boilers eliminate the need to heat and store large amounts of water in the tank.
- Cost savings: While any central heating installation cost is a hefty investment, a new combi boiler can reduce your bills by £50-£100 annually.
- Addressing existing issues: If your current heating system causes poor ventilation, which leads to mould or inefficient heating, a new combi boiler can resolve these issues.
Apart from those, you can also save on your new combi boiler installation costs (depending on your setup). Combi boilers forgo the need for complex pipework, making them simpler and cheaper to install. A cheap boiler installation is usually the most cost-effective option to heat a home, so you can check which combi boiler you can get for less.
What to consider when installing a combi boiler
However, even the most praised combi boiler out there can be a wrong fit if you don’t think your heating project through. Here’s a list of potential considerations before installing a combi boiler.
- Installation: First and foremost, your installation should be performed by a qualified heating engineer who will comply with relevant building codes and standards, such as BS 6798, for condensate pipe installations.
- Incoming water supply: Combi boilers require a minimum of 1 bar of pressure and at least 10-16 litres per minute flow rate. If the water pressure is too high, it’s recommended that you balance the system with a reducing valve.
- Existing pipework: Consult a plumber or gas engineer to check whether your existing pipework needs to be adjusted for high pressure (which is needed for combi boilers to operate).
- Gas supply: For a gas combi boiler installation, you may need to update or increase the gas pipe size, as it usually needs to be upgraded to 22mm minimum.
- Venting requirements: Plan for proper exhaust and air intake through an exterior wall.
- Hot water demand: Since combi boilers may struggle to supply hot water to multiple outlets simultaneously in bigger houses, choose a boiler that will suffice your household size (an output of 30-35kW is recommended).
However, while these points concentrate on the installation process, it’s important to factor in the removal of existing system components. Thus, if you convert from a regular system, you’ll need to remove tanks, cylinders, and redundant piping. Remember to consult a heating engineer regarding your heating project before making any decisions.
When to get a new combi installed?
If you’re without heating and hot water, then your reasons for getting new boiler quotes are quite straightforward! However, you shouldn’t wait for your boiler to break down to opt for a new combi boiler installation. There are many signs that you need a new boiler.
Some of the signs indicating you might need a boiler replacement include:
- Ageing boiler: The average boiler lifespan is somewhere around 10-15 years. So if your boiler has been in use for over 10 years, it might have outlived its usefulness and efficiency.
- Rising energy bills: Modern condensing boilers are more efficient than non-condensing boilers. If your gas bills rise without the energy prices increasing, then it’s a sign that your current boiler isn’t energy efficient and uses up to 20% more fuel to produce the same amount of heat.
- Frequent repairs: If you keep facing the same issues, such as low water pressure, thermostat issues, or broken components, this might indicate your boiler is becoming unreliable and needs replacement.
- Safety concerns: If your boiler produces water or steam leaks, detectable gas odours (for gas boilers), unusual noises (whistling or banging), or pilot light problems (such as frequent extinguishing or changing colours) - these are all alarming indicators to have your boiler inspected and replaced immediately.
- Declining efficiency: If your hot water takes longer to heat up or doesn’t reach the preferred temperature, this might be due to problems with a thermostat, diverter valve or heat exchanger. And these are signs of reduced boiler efficiency.
- Inconsistent heating: If you notice that some rooms in your house are colder or take longer to heat up, this might be due to a weakening pump, scale buildup in the heat exchanger or burner modulation issues.
If any of these signs sound familiar then it’s time for a new boiler. The best time to install a new combi boiler is during the warmer months, like spring or summer. Heating engineers are typically less busy and can offer better availability and prices. On top of that, many boiler brands offer summer sales which increases your chances to get a better deal.
Find the right combi boiler installer near me
A gas boiler installation has to be carried out by a Gas Safe registered engineer to ensure it meets building and safety regulations. If you need an oil boiler installation, you should find an OFTEC-registered engineer.
Only engineers listed on the Gas Safe register are legally allowed to work with gas appliances. You can check if an engineer is on the Gas Safe register on the Gas Safe website and should always ask to see an engineer's Gas Safe ID before they begin work in your home. The ID will not only confirm that they are competent but also which types of appliances they are able to work on.
Comparing quotes from multiple engineers is the best way to keep the costs of your new combi boiler installation down and ensure that you’re getting top advice. Instead of spending hours looking up the costs of different installers, let us help you get started in just 30 seconds.
Simply fill in our short form and wait for up to 3 engineers in your area to reach out to you with quotes for their services. Once you've received your quotes, compare them to find the right person for the job and secure the best deal for your new combi boiler installation. Thanks to our service, you will get to work with only the best professionals and save hundreds on your heating bills.
Click the button below to find a trustworthy engineer for your combi boiler installation.
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- Quotes from local engineers
- Get quotes today, installed tomorrow
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- Save up to £500 on installation
1,8 million quotes provided in 10 years
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FAQ
Are combi boilers easy to install?
Yes, combi boilers are fairly easy to install and the process can be finalised in about 1-2 days. However, in some cases the installation process will be more complex depending on the kind of combi boiler you choose and what type of boiler swap you require.
Can I install a combi boiler myself?
It is extremely ill-advised to install your own combi boiler because it can be dangerous for you and your home. It's best to find a Gas Safe registered engineer to help you.
How long does a combi boiler installation take?
Combi boiler installation can be as quick as 4 or 6 days, while more extensive heating system replacement can take upwards of 2 days. This timescale can depend on a few factors that may take longer, but generally, they are quick to install.
What happens during a combi boiler installation?
An engineer will come over and look at your home setup, assess the work that needs to be done, and provide you with a quote. Once you agree to a price, they will prepare your home, install it, and show you how to operate it. The process for replacing a system can be different but involves many of the same steps.
Can I replace my old boiler for a combi boiler?
Yes, you can! It's not out of the ordinary to swap one type of boiler for another but the price of the installation can vary on the type of boiler that needs to be replaced.