What is a Combi Boiler?

A combi boiler is an energy and space saving contraption that functions both as a central heating boiler and a water heater in one compact unit. So, the term combi is short form for combination which refers to the two-in-one aspect of the boiler.

Since the unit heats your tap water and supplies adequate heat for central heating, you don’t need a storage cylinder for hot water or tanks in the loft. This makes it space saving-one of the reasons most households in the UK use combi boilers. If you have no space for a hot water tank or storage cylinder, don’t worry since a combi boiler will serve you much better.

combi boiler

The difference between combination boilers and other conventional boiler systems is that combi boilers don’t heat water and then store it in a tank for use. Instead, combi boilers do heat water while you use it.

Thus, you don’t need another tank, which means less pipe work. These units allow you to access unlimited hot water, anytime you need it, and this can cut down your utility bill by at least 15 percent.

If your home has more than one bathroom, you may experience a slight decline in the combi boiler pressure if more than one of your appliances uses the boiler concurrently.  However, you can avoid this by not using many appliances at the same time, which can strain the boiler. Later on, I will let you know how you can easily boost water pressure when using a combi boiler.

Besides, some combi boilers perform better than others in terms of adjusting the pressure of water.  Certain models work well when it comes to combating performance decline due to straining the system’s use.

Why do Many People Prefer Combi Boilers?

If your existing unit is acting up, it’s time to consider a combi boiler installation. You need to know the advantages that come with using such a unit. If it’s your first time to use these boilers, they may seem a bit unusual. But if you do your due diligence, you’ll realize they have many benefits (read on to know these benefits) than the conventional boiler, which makes them a preference for most homes in UK.

You Don’t Need a Hot Water Tank

We all know the amount of room hot water tanks occupy. If your residence is not spacious enough, you will enjoy the lifestyle and privilege of having constant hot water without necessarily adding another tank for hot water storage. Combination boilers will heat up your water the way you need it. This means you’ll always access hot water and you’ll only need a small space to install the boiler.

Easy and Cheaper to Install

I know you have probably installed one too many appliances in your home that almost broke the bank. And so, the thought of installing another boiler makes you cringe. Why? Well, it’s because the cost of installation can be sky high.

combi boiler

But maybe you are forgetting the fact that installation costs can go high when there is a water tank involved. But this is not the case when it comes to a combi boiler since it takes care of your hot water supplies plus central heating needs.

So, this translates to a faster installation meaning it takes a shorter time and not so much labour. It also means fewer pipes will be used, and so you’ll save money and time on installation. So, in a nutshell, you save in the following ways:

  • No cost of the tank to think about
  • You can reduce the amount of pipes you’d need to pay for
  • The combi boiler installation takes a shorter time meaning you won’t pay the installer for many hours worked.

So, as you can see, you’re saving a lot of money in every possible way, isn’t it?

The Main Features of a Combi Boiler

  • Compact size, making it fit in a limited space
  • Hot water can be accessed on demand
  • Doesn’t have a bulky water cylinder
  • Eco-efficient models are available, allowing you to save up to £340 a year
  • The Energy Savings Trust recommends it since by using it, you can save approximately £340 a year
  • No emersion heater when in an emergency
  • Allows you to only heat the water you use
  • It’s the most popular boiler choice in UK
  • Using more than one tap can lower combi boiler pressure (which can be improved)
  • Heats both domestic hot water and central heating

What Determines the Cost of Combi Boiler Installation?

What about for those of us who have an old water tank in the loft that the engineer will need to remove? Of course, that will be more work on the engineer’s part and you’ll agree on what to pay for the extra work. The same applies if you need the engineer to remove a cylinder from the bathroom.

combi boiler installation

The other factors that determine the cost of combi boiler installation include the boiler’s size. The size may depend on your home’s overall size and the number of rooms in it. Be careful when choosing the boiler size as it can have a greater impact on your home’s energy bills.

Additionally, you may need to know whether the radiators require replacing and the length of the flue required to vent out the waste gases. Besides, installation may depend on the company providing the installation service and the area where the boiler should be installed.  If you are not sure about the size of the boiler that will suit your home, feel free to contact us for advice.


We have seen how practical combination boilers are. But the economical side of these boilers is worth looking at. Since this is a high efficiency boiler for you, you will save on your energy bills once you install it. Provided you go for an energy efficient model, you will see a decline in heating bills.

You’ll receive and use hot water constantly, at mains pressure. So, when you receive a quick call to rush to a meeting or pick a visitor from the airport, you will be able to take a quick bath, without waiting for the water tank to supply the water you need. Thus, you can enjoy a power shower anytime.

As you can see, having a combi boiler comes with many perks. If you have a hot water tank, it might seem strange to put it aside and have a combi boiler, but soon, you’ll get used to it. Having hot water on tap throughout the day is something your family will be happy and excited about.

So, if your existing boiler is about to give up (or has already given up), you should consider how much a boiler can help you save and how it can make life easier.

So, if you invest in a combination boiler, you stand to benefit in the following ways:

  • Reduced energy bills
  • User-friendly controls
  • Instant access to hot water
  • No tank in your loft
  • Reduced carbon dioxide emissions
  • Occupies a small space
  • No storage cylinder
  • Easy to install
  • Increased water pressure and power showers
  • A broad array of models to choose from

Aren’t these the benefits every homeowner wants to enjoy? Invest in a combi boiler today and you’ll see the difference.

How Does a Combi Boiler Work?

A combi boiler has been designed to provide instant domestic hot water for your showers and taps. It also provides hot water to the central heating system.  So, how do these boilers heat your water? Well, the boiler takes water from the mains and heats it as required, but it will be on standby whenever there’s no demand for water.

This ensures that you access hot water 24/7 and this water flows at the mains pressure. If your home has enough mains water pressure, you don’t need a pump to enjoy the power shower experience.

As the cold mains water flows through the pipes, it passes over a powerful heat exchanger. In the heat exchanger, gas is burnt to generate heat. The heat exchanger then transfers at least 90 percent of this heat to the cold water which is then delivered to the taps. This is what makes a combi boiler to be more energy-efficient than other boilers. Unlike the hot water storage tank which may lose heat, a combi boiler doesn’t have associated heat losses, as the water is heated as needed.

Aside from heating water in the taps, a combi boiler pumps water round your heating system, creating a fully sealed system. The boiler has an inbuilt expansion tank, and so there is no need to have an external feed or expansion tank in your loft, and this saves a lot of space, not to mention money.

It is worth noting, however, that a combi boiler works to produce central heating and hot water simultaneously. Thus, whenever you open a hot water tap at home, priority shifts to your domestic hot water. For instance, if you’re running a bath, hot water won’t circulate through your heating system, but when the bath is full, your central heating system will resume. This is one of the combi boiler problems (more on that in the next section).

These days, condensing boilers are the most installed ones. The boilers use heat contained in exhaust gases, which would typically be released to the atmosphere through the flue. They leverage on the heat exchangers to utilise this latent heat, and so heating the water requires less fuel. Consequently, it will reduce your fuel costs.

Combi Boiler Problems (and Their Solutions)

Hot water flows at the mains pressure, and if this water is required in different outlets concurrently (e.g. a washing machine and shower are running simultaneously), the different outlets will experience pressure drops. Luckily, you can fix this problem in two possible ways.

First, you can install a mains booster which will detect when flow and pressure are low and automatically increase the pressure of the incoming water from the mains. And the second option is to install the accumulator tank – a steel vessel which stores mains water and supplies it to the home at a high pressure.

The mains water compresses air within the steel vessel. When you open the tap, water can rush from the vessel to the tap at a faster speed than the mains water can flow to the property. The accumulator tank’s main shortcoming is that once there is no more water in the tank, you will go back to the same low combi boiler pressure that was there before introducing the tank.

Combi Boiler Control

A combi boiler has control valves inside it that operate it. When domestic hot water (DHW) is in use at home, the central heating system stops functioning and diverts all power inside the boiler to heat up the DHW. When the water is no longer in use, the power reverts back to heat your home’s central heating. However, the water and heating can’t be in use at the same time. This occurs flawlessly and normally, you won’t experience any heat loss in your home.

How Does the Combi Control Your Heating?

A thermostat controls the combination boiler and allows you to set your preferred room temperature. If the temperature declines below the set level in your home, the thermostat will trigger the boiler and the central heating will heat up your home to the level you prefer. If the room turns out to be too hot, the thermostat will trigger the boiler to go off.

Combi boiler Cost vs. Other Boilers

Perhaps, time has come where your existing boiler malfunctions and the part you require is not available. Or maybe you want to avoid all those problems by replacing your boiler before it stops working. Either way, it’s a bit tricky to know the exact amount you should pay. Here are more reasons to get a new boiler.

When Should You Go for a New Boiler?

  • If your boiler is in a state where repairing it is still costly (if you need more than £500 to repair it), you should think of getting a new one. To establish this, you will need to contact a competent engineer to inspect the boiler. If after checking it, he tells you that it is beyond repair, you may want to invest in a replacement.
  • If the boiler doesn’t control your heating the way you need it to; for instance, the timers and control may not be flexible or there’s no thermostat to regulate the temperature and heating. In that case, you may need a new boiler to help you save on your heating bills. In some cases, you may get away with installing new controls only.
  • If your heating system has a ‘dry cycle’. This is a common feature on older boilers meaning that if the heating is on yet your home is at the temperature that you set on the thermostat, it won’t turn off, but will instead send the heat to the overflow radiator (normally in the bathroom). This can waste enormous energy as you will be heating your home when there is no need to. A combi boiler is a perfect replacement here.
  • If your boiler shows a pilot light all the time, you may need to replace it. Well, a pilot light refers to the flame commonly seen burning, which you can see through a small window located on the front side of certain boilers. It is very common on old boilers and it wastes a lot of gas. You need to consider an energy-efficient model.
  • Is your boiler on the floor instead of the wall? That means it is certainly older and less energy-efficient. If that is the case, you should consider replacing it.
  • If you are planning to sell your house or renovate your home, you may need to invest in a new boiler, as it will add considerable value to your home. Prospective home buyers always consider whether they will be able to save on the home’s heating needs.
  • If your existing boiler is G-rated in terms of energy efficiency, consider replacing it.
  • Flue problems – While the flue is useful in terms of function and safety, repairing one is costly and you should rather spend that money on a new boiler.

What Determines the Combi Boiler Cost?

Why do some people pay under £2,000 to get a new boiler while others have to part with £4,000? The only way to get the difference is to understand the costs involved.


It all starts from the installation stage and determining how much it takes to install a boiler depends on various factors. First, the size of your boiler comes into play; if you live in a small flat, for example, you will require a smaller boiler than someone staying in a large house. That means the cost of buying and installing the boiler for your small flat will be low as well.


Other than the size, the boiler’s price also depends on the boiler type and brand. Typically, the cost of a new boiler can be anywhere between £500 and £2,500. But most importantly, the cost of buying and replacing a boiler can be compensated by the energy savings you get while using the boiler, thanks to the latest energy efficient boilers. If you choose to buy a new boiler to replace the old one, you should expect to save money on gas bills. The savings you will make are likely to outweigh the boiler replacement or installation costs.

If you would like to buy a boiler that is similar to the existing one (for example, your current boiler is a combi one and you want to replace it with another combi), The buying and installation cost may start at around £1300 as long as there are no major plumbing adjustments to be made. Typically, the combi boiler installation cost is within the range of £600 and £1000, and you will need to add the boiler cost to that.

On the other hand, if you would like to replace a regular boiler with the combination boiler, the installer will need to change pipe work and possibly help you to do away with the old tank. Thus, the cost of buying and installing this boiler may start at around £1800.

All of the prices mentioned above are just the starting point. The final prices will be influenced by the other factors including:

Gas Pressure

Always ask your heating engineer to check the gas pressure getting to the boiler; if it’s insufficient, it may lead to problems later on. A common issue is when the pipe used to transport gas from the mains meter to the boiler is too narrow. If the pipe coming from the meter is narrow (15 mm or less), chances are you may incur additional costs.

Moving the Boiler

At times, you may need to shift a boiler from one position to another. This is especially if the boiler is an old floor-mounted one, it is a back boiler or it is in unsuitable place (typically, boilers are now located on the external walls). In that case, the boiler will require major rerouting of the piping, and further you need to move the boiler, the more costly the job.

Flues and Building Regulations

Legislation has been changing over the years, and so a boiler installation three decades ago may fail to meet the latest standards. If the flue releases waste gas to a street, for instance, you may require a plume diverter to prevent the emissions from affecting people.

Besides, if you have a boiler mounted right at the centre of your house and its flue goes up the chimney, it won’t meet the current regulations. Accordingly, the boiler will require repositioning to an external wall.

Thus, if you want the new boiler to be in the same place, odds are you will be replacing a conventional boiler without a condense pipe with a new, condensing boiler. As such, the condense pipe may need to head to the sink, gutter or downpipe.

The difficulty one has to undergo while swapping these boilers may add to the job’s cost. If you have that old asbestos flue, you may need a specialist to remove it before installing the new boiler.

Heating Controls and Radiators

Replacing or adding radiators will certainly make the task more costly. Fortunately, you don’t necessarily need to change them, and if you are getting a combi, you will find it easy to remove the old tank. It also recommended that you get heating controls – thermostat and programmer. Additionally, for a larger property, thermostatic valves on radiators (TRVs) are recommended.

A thermostat and programmer may cost you a few hundreds of pounds whereas a TVR for each radiator may cost at least £50. If the thermostat or programmer is outdated or the thermostatic valves are missing, you should get them replaced. They are inexpensive and will pay back fairly fast.

The Installer

Price varies from one installer to another. While the workmanship of boiler installers across the UK varies, I would recommend that you go for a Gas Safe installer-such an engineer has been proved to ensure they are qualified to work legally and safely with gas. Gas Safe is the most recognized mark of quality for installer and it has replaced the ‘Corgi Registered’ mark.

So, when you buy the boiler, find out whether the seller offers installation services as well and if they do, ensure they are Gas Safe. An installer must have an ID card listing the gas work that they are qualified to carry out.

How Much Should You Expect to Pay as Combi Boiler Installation Cost?

The cost of installing boilers varies greatly based on the amount of work needed, your geographical location, the parts needed and whether they are available, and who you hire to do the installation.

best combi boiler

Which? Breaks down these costs according to different categories as follows:

1. Replacing a gas condensing combi to the position of the previous one

The work entails removing and taking away the old boiler before you install the new one.

Expected amount to pay is about £540 to £660

If you have a very cold heating system, you may need to add a mechanical flush, and this will cost approximately £510. The job here will involve adding chemicals to the heating system to clean it. The chemicals are then flushed out of the pipes using a mechanical pump.

  1. Buying a condensing boiler (combi) to replace a non-condensing one in the very same position

Prior to installing the combi boiler, the fitter should check out the flue position and the gas supply. The fitter may need to replace or remove the flue to fit the operation of the new, combi boiler.

Expected combi boiler cost in this case is about £640 to £770

Moving the pipe work may increase the budget by around £200 – £300. Very old systems need a mechanical flush prior to the combi boiler installation and this can cost about £510.

  1. Installing a combi boiler in a different location and adding controls and radiator valves to your heating system

The entire process is an involving one and may include routing the flue and adding a condensate.

Expected amount to pay is about £1,140 to £1,440

The heating system will also require a chemical flush which entails adding cleaning chemicals to it to eliminate debris. Chemical flushing can cost around £200.

4. Replacing a gas heat-only boiler with a combi (condensing) coiler

The fitter will be tasked with changing your system from the existing open-vented setup to the sealed one. The process may involve doing away with outdated equipment such as the cold water storage tank, hot water storage cylinder, and the feed and expansion tank within the loft.

Adding a condensate drain and re-plumbing may also boost the overall cost.

The expected combi boiler cost is about £1,440 for this job.

Besides, you may require extra pipe work (about £200 to £300) and a mechanical (about £510) or a chemical flush (£200) of your heating system.

So, to come up with the right cost for your boiler, you should:

  1. Choose the type and size of your boiler
  2. Add the estimated combi boiler installation costs
  3. Be ready for possible extras.

What Type of Boiler Should You Choose?

The three major gas condensing boiler types to choose from include:

  1. A combi boiler – heats water when you need it and doesn’t require you to install a storage tank
  2. A heat-only boiler – Also known as a conventional boiler meaning you need a cylinder or hot water tank to store hot water for later use.
  3. A system boiler – It’s similar to a heat-only unit but has more in-built components. They are easy to install than the conventional types and they occupy less space.

If you reside in a small home with one bathroom, your best bet will be a standard combi boiler. However, if you reside in a larger home, you may consider the system or heat only boiler. But remember, a boiler can suit even larger homes with a few modifications to improve on combi boiler pressure when operating different outlets, as discussed earlier.

Still undecided on what may work for you, get in touch with us and an experienced heating engineer will advise you on the best choice.

Looking for the Best Combi Boiler?

If you are swapping a conventional unit with a modern gas condensing boiler, you are on your way to saving a good amount on your energy bill. According to the recent estimates on savings, if you reside in a detached home and are buying a condensing boiler to replace the old-style one, you will save about £652.

If you would like to replace your modern condensing unit, you will find both of them to be energy efficient. When you look at the condensing boilers from the greatest 11 manufacturers across the UK, there is a minor difference in efficiency.

According to the (SAP 2009) industry standard, the most efficient boiler has a rating of 91.0 while the least efficient one has a rating of 88.2. All the boilers analysed have an average efficiency of 89.2.

So, obviously, a combi boiler is the most convenient, energy-efficient, and reliable boiler your home needs. Get yours today and start saving money as you enjoy its heating service for many years to come.

Best Combi Boilers

Typically, we have electric combi boilers as well as those that use gas or oil. And for the most part, the combi boiler installation may cost more than acquisition of the equipment. But if you get the best combi boiler, you will enjoy hot water and home heating for many years to come.

Over time, you save on energy costs and get back the initial purchase and installation costs of your combi boiler. So what is the best combi boiler in UK? Well, if you go through different combi boiler reviews, you will realize that the best ones include:

  • Worcester Bosch combi boilers
  • Baxi boilers
  • Vaillant boilers
  • Glow Worm boilers
  • Potterton boilers

1. Worcester Bosch Combi Boiler

When shopping on the Internet for various boilers, you might get confused regarding the different guarantee periods available, and particularly when they all seem to address the same product. The Worcester combi boiler has the leading guarantee in the market – it covers up to 8 years after an accredited engineer installs it.

Unlike other guarantees out there, it will cover you if anything ever goes wrong with your boiler.  Remember to get a quote from the installer to find out the guarantee service type specified before they start fitting the boiler.

Worcester Combi Boiler

In 2014, Worcester Bosch received a Which’s ‘Best Buy’ for the fourth year in a row. They are known to be among the most reliable and quietest boilers for homeowners.

Worcester sells four main types of combi boilers namely:

  1. Classic

A classic boiler has the broadest array of features and its central heating output is 30kW. It can control both your central heating temperature as well as hot water, giving you more control and flexibility.

  1. Compact

They are the smallest boilers with the highest efficiency. They can fit in a kitchen cupboard, and their output will amaze you – 24kW.

  1. Junior

They suit smaller properties with only one bathroom. They have an output of 24kW and give great results although with a lower flow rate of water and less flexibility.

  1. Highflow

They are bigger, can stand on the floor, and work well in homes with several bathrooms. Their output is 30kW and their flow rate can be high when there is good mains pressure.

Worcester Bosch Combi Boiler Cost

Worcester combi boilers can cost from around £700 and above. If you would like to buy the classic type, expect to pay about £1200. Compact models can cost a bit more.

2. Baxi Boilers

Baxi is a boiler brand based in East Midlands. Richard Baxendale and Joseph Held founded it in 1866. It’s one of Europe’s biggest boiler manufacturers. It is part of BDR Thermea that includes Main and Potterton boiler brands.

baxi combi boiler

Baxi has a number of combi boiler ranges which include Baxi Platinum HE A, Neta-tec GA and Baxi Duo-tec GA. The other boiler ranges produced by Baxi include Baxi Bermuda back, Baxi Magaflo compact system GA, and Baxi Solo heat-only. These ranges have various individual products.

What is the Cost of a Baxi Boiler?

The cost of a Baxi boiler can be within the range of £ 700 and £ 1,170, and it depends on the type and size of the boiler.

Warranties and Servicing a Baxi Boiler

Most of these boilers come with a warranty of two years, but you can find limited time offers that may go up to 10 years. Registering a Baxi warranty is easy: you can either visit the Baxi website to register or fill out the registration card that you are given at the time of buying the boiler.

Baxi Combi Boiler Price Range

Baxi combi boilers do provide on-demand hot water and central heating. It is not only energy efficient, but will also save your space and money in the long-run, making it the best combi boiler for most homeowners. The combi boiler cost here is within the range of £ 730 and £ 1150 with varying dimensions, flow rates and outputs.

3. Vaillant Boiler

Vaillant is a German brand that has been around for over 135 years. Its products are sold in over 80 countries and this includes the UK.

vaillant combi boiler

Vaillant has different types of combi boilers that provide instant hot water and heat. The first one is EcoTec Pro that suits smaller homes. We have the EcoTec Plus range with three power levels – if you have many hot water taps, you will need a higher power.

What is the Range of Vaillant Boiler Prices?

Depending on the size, type, dimensions, outputs and flow rates, Vaillant combi boilers can cost anywhere between £ 875 and £ 1305.

4. Glow Worm Boilers

Glow Worm is one of the UK’s leading boiler manufacturers. Glow Worm has over 75 years in the heating industry. It produces highly energy efficient boilers that have reduced heating costs and carbon emissions. The highly prestigious Which? Gave Glow Worm boilers a ‘Best Buy’ award.

Glow Worm Combi Boiler Cost

In the UK, Glow Worm Flexicom boilers are known to have a direct rear flue option. Thus you can install the Flexicom combi boiler nearly everywhere. New Glow Worm boilers come with extensive flueing options that encourage flexibility when it comes to fitting. The Glow Worm combi boiler prices are between £ 624 and £ 1309. Besides, they come in diverse sizes with varying outputs and flow rates.

5. Potterton Boilers

Potterton, a British company has been around for the last 150 years. Many people know this brand because of its reliability, which of course, applies to their boilers, their customer service and other products. They are known to supply highly efficient boilers and so Potterton is a company you can fully trust.

potterton combi boiler

Potterton Combi Boiler Cost

The range of Potterton combi boilers starts from the Potterton Gold Combi HE A, which is their flagship product. Like other combination boilers in UK, this boiler supplies heat to radiators and also to the domestic hot water when needed. They are easy to install and occupy little space. Potterton combi boilers are reasonably priced and highly energy efficient. Their price range is between £ 640 and £ 996. They come with different outputs and flow rates.

Getting Your Best Combi Boiler

Now you know the best combi boiler for your family. So, out of these five of the best combi boilers, you can go for what suits your pocket, home size and heating requirements. These units have been tried and tested for many years to be the best heating solution for households in UK.

Whether you are looking for an electric combi boiler or one that uses gas, you’ll find something that suits you. Remember to check out online combi boiler reviews to learn a thing or two about your next decision. Are you uncertain of the best combi boiler to choose? Let us know and we will give advice to help you make a wise decision.