Updated: May 2, 2024

What are combi boilers? 

Combi boilers have surged in popularity in recent years, especially for average-sized homes. But what exactly are they and how do they function?

The term “Combi” is short for combination boiler. Unlike older systems that rely on immersion heaters drawing from a tank, combi boilers serve both hot water and heating needs in a single unit.

With traditional systems, hot water wasn’t always readily available on demand. Preheating was often required, leading to inconvenience and higher operating costs. Additionally, these older systems tend to be bulkier, requiring significant space for installation.

Why are combi boilers so popular? 

Combi boilers excel in efficiency due to their dual functionality of providing hot water and heating. Green Combi boilers, in particular, boast exceptional efficiency, with some models reaching up to 98%. Their compact design makes them ideal for homes with limited space, and they can even be installed inside kitchen cupboards for added convenience.

What are the Advantages of Combi Boilers? 

Space-Saving Design: Combi boilers combine heating and hot water functions in a single unit, saving valuable space in your home compared to traditional boiler systems.

Energy Efficiency: Combi boilers are highly efficient, with many models boasting high energy efficiency ratings. This can lead to lower energy bills and reduced environmental impact.

On-Demand Hot Water: With a combi boiler, hot water is available on demand, eliminating the need for a separate hot water storage tank. This ensures a constant supply of hot water whenever you need it.

Quick Heating: Combi boilers heat water directly from the mains, providing fast and efficient heating for both hot water and central heating systems.

Reduced Installation Costs: Because combi boilers do not require a separate hot water storage tank or cylinder, installation is often simpler and less costly compared to traditional boiler systems.

Convenient Operation: Combi boilers offer convenient operation, with many models featuring programmable controls and advanced heating technology for optimal comfort and convenience.

Flexibility: Combi boilers are suitable for a wide range of homes, from small apartments to larger houses, making them a versatile choice for many homeowners.

Read about : Top UK Combi Boilers

Best combi boilers & boiler brands

What are the Disadvantages of Combi Boilers? 

It’s worth mentioning that their advantages outweigh the disadvantages 

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.  

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… 

  • Perfect for homes with limited space  
  • A hot water storage cylinder and a cold water tank are not needed  
  • Unsuitable for larger homes with many bathrooms or a high demand for hot water  
  • Inadequate for places with low water pressure  

The right Combi Boilers size for you. 

When discussing boiler size, we’re referring to its power output, not its physical dimensions.

The unit of measurement for Combi Boilers is kilowatts (kW). In simple terms, the higher the kilowatts, the greater the boiler’s capacity to meet your hot water and central heating needs.

For small homes with just one bathroom, we recommend opting for a small (low power) combi boiler.

Conversely, larger properties with multiple bathrooms will require a larger boiler to adequately meet the increased demand for hot water and heating.

Combi boilers common faults  

types of Gas Boilers

Vaillant Combi Boilers Reviews

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

NO. OF BEDRROMS 1 bath & shower 2 baths & showers  
2-beedrom house 26 kW 29 kW Get Quotes 
3-bedroom house 29 KW 35 kW Get Quotes 
4-bedroom house 29 KW 35 KW Get Quotes 
5-bedrrom house 35 KW 35 KW Get Quotes 

How do Combi Boilers work? 

Cold water flows directly through the combi boiler from the main water source, while gas fuel is burned to generate heat. This heat is transferred from the combustion chamber to the water via a heat exchanger.

Your thermostat detects temperature drops in your home and signals the combi boiler to ignite and heat your house accordingly.

Once the desired temperature is reached, the combi boiler reduces heat production to maintain the set temperature, minimizing energy waste and keeping your home warm.

A combi boiler directs hot water to any outlet in use, such as a hot tap, shower, or bath. When the tap is turned off, the central heating resumes operation.

It’s important to note that a combi boiler can supply hot water to either the water outlets or the central heating system at a time, but not both simultaneously.

Is a Combi Boilers the perfect choice for your home? 

Combi boilers draw water directly from the mains water supply in your home and rely on mains pressure to provide adequate water flow.

Therefore, if the mains pressure is insufficient, a combi boiler may not be suitable for your home.

Combi boilers have two outputs: one for hot water and the other for home heating. Heating water for central heating requires less effort than providing on-demand hot water. It’s crucial to select a boiler that matches your hot water demands accordingly.

If you reside in a large home with multiple bathrooms, a system boiler may be more suitable for your needs.

Read about:

Viessmann Combi Boilers Reviews

Affordable Boiler Prices

Best combi boilers & boiler brands

What is meant by a Condensing Boilers? 

The terms “condensing” and “non-condensing” can be perplexing for those in the market for a new boiler.

Currently, it’s mandated by law that new boilers must incorporate condensing technology. This means you needn’t worry about specifically seeking out a condensing boiler.

Condensing technology isn’t a boiler type, but rather a technical feature. In a condensing boiler, a larger heat exchanger is utilized, allowing for the extraction of additional heat from the fuel. This results in heightened efficiency compared to non-condensing boilers, as they capture and utilize heat that would otherwise be lost in the exhaust gases.

Non-condensing boilers, on the other hand, are considerably less efficient, losing around 50% of heat through combustion exhaust gases. In contrast, condensing boilers capture and utilize this excess heat to heat water, thereby significantly improving efficiency.

Condensing boilers boast an energy efficiency rating of up to 90%, utilizing surplus energy to heat your property. Moreover, they are environmentally friendly and can help reduce your heating bills.

Read about:

Baxi Combi Boilers Review

 How long will a combi boilers last? 

Boilers vary in quality and lifespan, which is an important consideration when purchasing a new one.

While opting for a cheaper boiler might seem like a way to save money initially, it’s not a wise investment in the long term. Low-quality boilers are prone to more frequent repairs, ultimately costing you more over time.

On average, combi boilers last between 10 to 15 years, but this can vary based on the quality of the boiler and how regularly it’s serviced.

You can gauge the quality of a boiler by examining the warranty it offers. For example, a boiler with a 10-year warranty typically indicates higher quality compared to one with a 5-year warranty.

Can I get the next-day boiler installation? 

You can have your boiler installed the next day with Cardiff Boiler Service. Just place your order before 12 pm during colder months or 2 pm in warmer months.

Our next-day boiler fitting service covers nationwide locations in England, Wales, and Scotland. You won’t have to endure prolonged periods without heating, even during the coldest winter months.

Few boiler companies can offer such rapid nationwide installation on short notice. If you’re in need of a boiler, request a quote from us as soon as possible.

best boilers in uk

How long should it take? 

Boiler installations can vary in duration depending on the scope of work required for each specific home or business.

Replacing an existing combi boiler with a new one typically takes around 3-6 hours.

However, if you’re replacing a heat-only boiler with a combi or system boiler, the installation process may take 1-2 days to complete.

  Installation energy regulations 

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

  • Gas boilers should have at least a 92% ErP efficiency regardless of boiler type. 
  • A Combi boiler installation should have one energy-saving feature. 
  • You should have functioning time and temperature controls. 
  •   So why Cardiff Boiler Service? 
  • Cardiff Boiler Service Are Quality & Accredited Boiler Installers 
  • Firstly, Cardiff Boiler Service 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 Cardiff Boiler Service 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 Cardiff Boiler Service 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. 
  • 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? 

  • We work in Cardiff and the surrounding areas of South Wales. 
  • We are reliable, professional and trustworthy. 
  • High Trustpilot score of 4.9 out of 5. 
  • We can travel anywhere throughout the UK. 
  • Gas Safe Accredited (corgi registered). 
  • Our finance is FCA accredited. 
  • We provide a 12-month snag guarantee. 
  • Our prices are very competitive. 
  • We make sure your house is kept clean and tidy during work. 
  • Our workmen use floor protection. 
  • We dispose of your rubbish correctly.