What are combi boilers?

Combi boilers are one of the most popular options for people to install in the recent years. If you are living in an average sized home, then combi boilers are your best choice. But what are they and how do they work?

The word Combi stands for combination boiler. This single unit both provide hot water and heating. That’s why they are better than older systems that consist of an immersion heater which uses water from a tank way up.

With the older system, hot water wasn’t always on-demand. To have hot water, you need to turn on the water heater in advance. Not to mention the high cost and the amount of money of operating these older systems. Furthermore, an older system is much larger and needs a lot of space.

Why are combi boilers so popular?

Combi boilers have two functions (providing hot water and heating). As a result, they are very efficient . Green Combi boilers are up to 98% more efficient. Their compact shape and design makes them perfect for homes with limited space. They can also be installed in kitchen cupboards.

How do Combi Boilers work?

Cold water runs through the combi boiler directly from the main water source. In order to produce heat, the gas fuel is burned. The heat is then transformed from the combustion chamber to the water through a heat exchanger.

Your thermostat would know when the temperatures drop in your house. Subsequently, it will send a signal to the combi boiler which would fire up and heat your home.

The minute the required heat is reached, your combi boiler would decrease the produced heat and keep the status quo. As a result, it will reduce your energy waste as well as keep your house warm.

A Combi boiler directs hot water to any outlet you are using such as a hot tap, a shower or a bath. When you turn off the tap, the central heating duties will be back in action.

Keep in mind that your Combi boiler directs hot water to the water outlets or the central heating, but not both at the same time.

Is a Combie Boiler the perfect choice for your home?

Combi Boilers take water directly from the mains water supply in your home. To provide an appropriate water flow, they rely on the pressure coming from the mains.

So if the pressure from the mains is not strong enough, a combi boiler is not, therefore, suitable for your home.

A combi Boiler comes with two outputs; one for how water and the other is for home heating. Hot water for central heating takes less effort than on-demand hot water. That’s why it’s crucial to choose a boiler that corresponds with your hot water demands.

Another key point is that if you live in large home with many bathrooms, then a system boiler is what you need.

The right Combi Boiler size for you.

When we talk about boiler size, we do not mean its dimensions, but rather its power output.

The unit of measurement, used for Combi Boilers, is the kilowatt (kW). To clarify, the bigger the kilowatts, the greater the capacity of the boiler to match your demands for hot water and central heating.

We advise that you get a small (low power) combi boiler if you have a small home with only one bathroom.

On the other hand, you will need a much bigger boiler if you live in larger property with more than one bathroom.

Here’s what you need to know about Minimum kW Size:

NO. OF BEDRROMS1 bath & shower2 baths & showers 
2-beedrom house26 kW29 kWGet Quotes
3-bedroom house29 KW35 kWGet Quotes
4-bedroom house29 KW35 KWGet Quotes
5-bedrrom house35 KW35 KWGet Quotes

The Advantages of Combi Boiler:

1. A combi boiler is very efficient

A combi boiler is very efficient when it comes to energy consumption. It would save you a lot of money since it can be used for both providing hot water and heating your home.

2. They are small in size

A combi boiler is perfect for a house that is small in size. You will not need to make space for water tank or cylinder due to that fact that a combi boiler takes water from the mains directly.

3. On-demand hot water

With a combi boiler you don’t need to worry about having enough water in the hot water storage. It will provide hot water instantly.

4. Installation Flexibility

Combi boilers are relatively small and consist of a single unit. As a result, they can offer more flexibility when it comes to their Installation place.

The Disadvantages of Combi Boilers:

It’s worth mentioning that their advantages outweigh the disadvantages.

1. The Flow Rate is Limited

Using two or more taps at the same time will reduce the water flow rate. For one thing, we don’t recommend a combi boiler for those who live in larger homes or those who have multiple bathrooms.

3. Relying on water pressure from the mains

A combi boiler heats the water coming from the mains. It won’t work adequately if your water pressure is low.

In conclusion:

The best combi boilers out there:

1 – Worcester Bosch Greenstar CDi Compact

2 – Viessmann Vitodens 050-W Combi

3 – Alpha E-Tec

4 – Baxi 600 Combi

5 – Ideal Logic+ Combi

These are the best types of boilers provided by some of the UK’s best boiler manufacturers. They are known for fantastic customer reviews, technical brilliance, warranty periods, power and efficiency.

How long will a combi boiler last?

Of course, boilers differ in quality and their lifespan. When buying a new boiler, it is important to keep this in mind.

You might be tempted to buy a cheap boiler in order to save some money. But this is not a good investment in the long run. A low-quality boiler will eventually cost you more on repairs.

In estimate, combie boilers last 10-15 years. But surely this will depend on the quality of the boiler you buy and how often do you have it serviced.

You can easily know the quality of a boiler from the warranty they offer. For instance, A boiler with a 10-year warranty have a higher quality than a boiler with a 5-year warranty.

What is meant by a Condensing Boiler?

The terms condensing and non-condensing can be confusing to people shopping for a new boiler.

Presently, it is stated by law that new boilers must use condensing technology. In short, you don’t have to worry about getting a condensing boiler.

Condensing is not a type of boiler, but rather technical feature. In a Condensing boiler you get a much bigger heat exchanger. They also produce additional heat from the fuel. The same fuel that would have been wasted in a non- Condensing boiler. As a result, they are more efficient.

non-condensing boilers are less efficient by 50% since a lot of heat was lost in the combustion exhaust gases. On the other hand, new boilers would capture this heat and use it to heat water.

condensing boilers are energy efficient by 90%. They use excess energy to heat your property. Not to mention, they are environmentally friendly and reduce your heating bill.

How long should it take?

Boiler installations can take different amounts of time to complete due to such a varied amount of work for each particular home or business.

Replacing an already-existing combi boiler with a new one should take 3-6 hours.

Replacing a heat-only boiler with a combi or a system boiler would take 1-2 days.

Can I get the next-day boiler installation?

Yes, you can get next-day boiler installation with Let’s Heat. If you order your boiler before 12 pm during the colder months, and 2 pm in the warmer months.

This is next-day boiler fitting nationwide in England, Wales and Scotland. So you do not have to be without heating for long, even in the depths of winter.

Not many boiler companies can fit a boiler at such short notice nationwide. If you need a boiler, get a quote from us as soon as possible.

Installation energy regulations

Over the last few years, the UK has passed some guidelines for boiler installation and energy efficiency:

Finance for your boiler installation!

Buying a new boiler and having a boiler installation is an investment. However, it can be expensive, especially paying for it all in one hit. You can get the job done on a finance package that is FCA-approved if you don’t have enough money on hand.

We can also offer a number of split payment options for you to consider.

So why Let’s Heat?

 A. Let’s Heat Are Quality & Accredited Boiler Installers

Firstly, Let’s Heat professional engineers and emergency plumbers provide a professional and reliable plumbing and heating service. Accordingly, that includes Boiler Installation in Cardiff and the surrounding CF postcode area in South Wales.

Secondly, our boiler installation and repair team is fully qualified and ensured to the highest standards. As can be seen, we take pride in producing exemplary work standards which include completing all boiler installation needs. 

Thirdly, the Let’s Heat team are high-quality professional engineers who have a high 4.9 out of 5 Trustpilot score by our previous happy customers. We are fully accredited by Gas Safe and Corgi registered, as well as FCA approved for all of our financial transactions. 

Lastly, all of our staff at Let’s Heat are experts in their field and have many years of experience. Above all, we have work on a wide selection of emergency plumbing, heating solutions and services throughout Cardiff, the rest of Wales & the UK.

B. Because we care

Are you still a little confused about where to start or who to use?

Our easy-to-use online questionnaire will help you with what you need to know. In short, We make sure that you have the correct solution for your needs. We will also ensure that you are completely happy with the solution.

Why else?

You can research your boiler installation needs and buy your new boiler and the boiler installation online without leaving the house.

If you need a new boiler, reach out to our experienced Boiler engineers team for more information.

We install boilers nationwide and include next-day installation (on orders placed before 12/2 pm in all seasons.)

In conclusion, Let’s Heat plumbers are experts in all aspects of boiler installation and repair. If you have any further questions, feel free to take a look at our FAQs or contact us.

Areas covered by our Boiler Engineers:

The Let’s Heat boiler engineers cover all of Great Britain including Wales, England & Scotland.


Let’s Heat provide Boiler Installation throughout Wales, including South East Wales, South Wales, South West Wales, Mid Wales, East Wales, West Wales, and North Wales.

This includes the cities of Cardiff, Newport, Swansea, and all other towns and cities in Wales.


Let’s Heat provide Boiler Installation throughout England, including South West England, South East England, East Midlands, West Midlands, North West England, and North East England.

This includes the cities of London, Reading, Southampton, Portsmouth, Bristol, Exeter, Plymouth, Gloucester, Swindon, Oxford, Leicester, Nottingham, Derby, Birmingham, Worcester, Wolverhampton, Walsall, Liverpool, Manchester, Leeds, York, Sheffield, Newcastle, Sunderland, and Middlesbrough, etc.

Have any further questions, please see our FAQ Page. Want to check our Gas Safe Registration or want to see our near 5 star Trustpilot rating, please click the links!