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Cost of Installing a Combi Boiler

Are you considering having a new combi boiler fitted? In the following article, we’ll break down how much different sizes and types of combi boilers would cost and how long the installation work might take.

We’ll also explore other relevant topics such as how you could install one yourself and the possible issues that may arise with installing a combi boiler.

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Introduction to Combi Boilers

A combi boiler comes in one compact unit which simultaneously acts as a central heating boiler and high energy water heater. As a result, they can provide heated water right away which is likely the leading reason for their popularity.

By combining two boiler types, it can also save money on installation costs and bills. This article will prove helpful if you plan to have a combi boiler installed in the near future or would like to know how much it would cost for future reference.

How Much Does Installing a Combi Boiler Cost?

Let’s start by taking a look at the average cost of installing combi boilers based on different type and power output. The price will vary depending on whether you’re having an old combi boiler replaced or if you’re installing a combi boiler in place of another type of boiler.

In the case of the former, a 24kW to 27kW combi boiler will likely set you back between £1000 and £2100, a 28kW to 34kW combi boiler will cost around £1000 to £2700 while you can expect to pay between £1250 and 3500 if you’d like a 35kW to 42kW combi boiler installation.

If on the other hand, you need to have another boiler type replaced with a combi boiler, you’ll need to add around £600 to £1000 to the above estimates for a new combi boiler price.

As for the cost estimates of combi boiler types, an average oil combi boiler installation should cost anywhere from £1800 to £4500 depending on the power output.

With the same reason for price variation, an LPG combi boiler fitting could set you back between £1500 and £3500, a gas combi boiler about £1000 to £4300 and an electric combi boiler roughly £2000 to £4000. The tables shown below break down these cost evaluations more precisely.

Gas Combi Boiler

Power Output (kW) Replace Old Combi Boiler Replace Other Boiler Type
24 - 27 £1000 - £2200 £1600 - £2500
28 - 34 £1600 - £2700 £1600 - £3500
35 - 42 £1250 - £3500 £1850 - £4300

Oil Combi Boiler

Power Output (kW) Replace Old Combi Boiler Replace Other Boiler Type
24 - 27 £1800 - £2600 £2400 - £3400
28 - 34 £2100 - £2900 £2600 - £3700
35 - 42 £2250 - £3700 £2850 - £4500

LPG Combi Boiler

Power Output (kW) Replace Old Combi Boiler Replace Other Boiler Type
24 - 27 £1500 - £2200 £2100 - £4000
28 - 34 £1750 - £2500 £2350 - £3250
35 - 42 £2250 - £2700 £2600 - £3500

Electric Combi Boiler

Power Output (kW) Replace Old Combi Boiler Replace Other Boiler Type
24 - 27 £2000 - £3200 £2600 - £4000
28 - 34 £2000 - £3200 £2600 - £4000
35 - 42 £2000 - £3200 £2600 - £4000

Labour and Supply Costs

A heating engineer will charge about £500 to £700 in labour costs to replace an old combi boiler. If you’d like to have another boiler type replaced with a combi boiler, the installation fee will land around £1100 to £1500.

Heating engineers tend to charge around £35 to £60 per hour depending on where you live. In London or the southeast of the country, you’ll find that labourers charge higher rates than the nation on average while it’s cheaper in regions such as the north of England.

As for the new combi boiler cost, it ranges from about £500 to £2800 in the case of a gas combi boiler, £1300 to £3000 for an oil combi boiler, £1000 to £1500 for an LPG combi boiler and £1500 to £2500 for an electric combi boiler.

The total cost can vary depending on the type and size of the boiler, whereabouts in the UK you live and ease of access to the installation area.

Types of Combi Boiler

Now we’ll lay out the details of different boiler types in more detail. In each of the following subsections, we’ll consider what each boiler type is, the different combi boiler prices and other aspects such as their pros and cons.

Gas Combi Boiler Costs

This type of combi boiler involves central heating systems which continuously heat water, acting like lots of small fires. A gas combi boiler either uses bulk LPG which is stored on site or on-grid gas. The gas will then be burned via the boiler’s combustion chamber. The water is warmer to approximately 70°C with a heat exchanger.

This type of combi boiler is the most frequently used. You’ll also get the lowest running costs with a gas combi boiler. The installation cost of a gas combi boiler will probably land between £1000 and £3500. Gas combi boilers can be the cheapest to have installed although it’ll depend on the quality and brand of the boiler in question.


✔ Most popular option

✔ Low running costs

✔ Powerful combi boiler type


✖ Installation can be difficult

✖ Requires a carbon monoxide detector

Oil Combi Boiler Costs

The next type we’ll consider is an oil combi boiler. With about 2 million households across the UK not linked to the gas grid, about three quarters of these use an oil combi boiler. In addition, it’s cheaper to use oil as your heating fuel instead of LPG or electricity.

The oil is ignited in the combustion chamber of the boiler and the heat exchanger moves this heat through to warm up the cold water. In order to install an oil combi boiler, you’ll need a tanker of oil fitted outside your property.

The tanker would also need to be refilled every so often. On average, it’ll cost you around £2000 to £3700.


✔ Great alternative to a gas combi boiler

✔ Cheaper than LPG or electricity


✖ You’ll need to refill a tanker periodically

Electric Combi Boiler Costs

Lastly, there is an electric combi boiler. This type works a bit differently to the other types we’ve looked at. An electric combi boiler takes a similar approach to heating water as an immersion heater.

Generally, these types of combi boilers are a last resort option, if other types aren’t practical or are too costly. Part of the reason for their limited popularity is that they are only suited to certain sized properties. Further, it can have high running costs.

However, electric combi boilers do have several advantages. For instance, they are entirely silent since its internal components do not work at a fast rate. In addition, they are energy efficient and more eco-friendly. The installation cost of combi boiler that is electric will be about £2000 to £4000.


✔ Generally cheaper fitting costs

✔ Won’t make a sound

✔ Energy efficient

✔ Eco-friendly


✖ Considered a last resort option for many

✖ Do not work during a power cut

✖ Not suitable for a large property

What Does a Combi Boiler Installation Involve?

Let’s now break down the steps involved in fitting a combi boiler. Since each type of combi boiler is different, the following process described is a general overview although we’ll mention at times how these steps may vary for each boiler type.

Step 1 - Surveying and Preparation

Before any work can get under way, a heating engineer will need to assess the location. This will help them figure out where everything can go, how the area can be accessed and how exactly they’ll need to approach the installation based on the design, type and size of your property.

Other considerations that a labourer will need to take into account are where the condensate pipe will go and where the flue will be positioned. If it is a gas combi boiler you’re looking to have installed, it’ll be essential that you have a 22mm gas supply.

If you wish to have an electric combi boiler installed, it’ll be important to establish first whether your property is suitable for this type of boiler. Ideally, this should be achieved before a heating engineer is called out.

Once the necessary assessments are complete, the contractor will prepare the installation area. Many tradespersons will place protective covers over the floor ahead of the work. A small amount of water spillage will be difficult to avoid. It’s also not uncommon for the central heating system to undergo a power flush before a new boiler is fitted.

Step 2 - Installing the Combi Boiler Inside the Wall

Next, the boiler itself needs to be fitted in place. It’s vital that fittings are secured and water and electricity are turned off prior to the instalment of the boiler. Exactly what the work will entail will depend not only on the type of combi boiler being installed but the type of boiler being replaced.

If your current boiler is a combi then once it is removed, the new combi boiler can be fitted into the wall relatively easily. Once in place, the water and fuel/energy supply can be reattached before the system is tested.

In the case of replacing another type of boiler, the old system will need to be disconnected first. Any gas and water connections which you will no longer require must be secured while the other boiler can be taken away. Water tanks, if present, can be removed at another point.

Then, the area of the new combi boiler needs to be prepared. It may prove necessary for the heating engineer to add new pipework for the drainage, gas works and water supply, depending on the type of boiler being fitted. Lastly, the boiler can be mounted and connected to its necessary links (e.g. energy/fuel supply). Once again, the system will need to undergo some testing.

Step 3 - Clean-up

Once the boiler has been tested and all seems fine, the clean-up process can get underway. This may or may not involve the old boiler being disposed of, depending on what you’d like to do with it once the new boiler is in place.

Additional Work You May Need When Getting a New Boiler

When having a combi boiler fitted, there is plenty of additional work you may wish to have undertaken at the same time. For example, you may wish to have new radiators fitted. To have an old radiator replaced will likely cost between £150 and £250.

If you’d like to have a new radiator added without an old one to replace, you’re looking at a price range of between £250 and £350. The price tag of moving a radiator on the other hand will probably end up around £120 to £180.

DIY Combi Boiler Installation

Unfortunately, fitting a combi boiler is not something you should do by yourself. Any boiler needs to be installed by a registered and experienced individual. The main reasons for this are for safety and to ensure that the work meets building regulations.

Further, in the case of a gas combi boiler, there are even more risks associated. Either way, it’s not a job that should be undertaken DIY. A registered contractor will be able to review the installation and make sure that everything is safe and working okay.

Potential Problems and Pitfalls

Having a combi boiler fitted can come with challenges. For example, your property or aspects of your property (e.g. the gas supply) may not be suited to a combi boiler. Even when installed, issues can arise in general with combi boilers. Such disadvantages include difficulties in meeting a high water demand and a relatively slow water rate.

As for common fixes, firstly, your boiler indicates lower pressure and you need to find a solution. If this is the case, you’ll need to look for the fillip loop which is generally beneath the boiler before turning the small tape in a counter-clockwise direction. If the pressure begins to rise again as it should, then once it reaches approximately 1.5 bars, you can turn the tap back in a clockwise direction.

If your combi boiler experiences a frozen or blocked condensate, first you should try pouring hot water from a kettle in an effort to thaw out the condensate. Then the pipe should be removed below the boiler before you can drain it into a bucket.

If the problem continues to repeat, consider having a condensate trace heater retro-fitted. If the heating fails to work, you may need to replace the batteries. If the replacement is complete within a minute, the settings you’ve selected for the temperature and time should remain. Otherwise, you’ll likely need to reset the combi boiler’s settings.

As for maintenance, cleaning dirt and debris from the boiler and repairing any parts which become damaged are essential steps in prolonging the life of a heating system. You should also assess its internal parts from time to time. The boiler casing should also be removed and cleaned from time to time.

Powerflushing is often required and may or may not be included in the cost of having a combi boiler installed. On its own, a power flush generally costs about £400. It’s best practice to have your combi boiler serviced at least once a year.

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Sam J

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