If you’re considering getting a new boiler, you might have heard about a “combi boiler.” But what exactly is it, and how does it work? In this article, we’ll break down what a combi boiler is, how it functions, and its pros and cons. By the end, you’ll have a clearer picture of this widely used heating and hot water system and whether it could fit your home well.

What is a combi boiler?

A combi or combination boiler is a nifty heating and hot water system that does it all in one neat package. First, it heats your home and supplies hot water without needing a separate tank. Then, when you turn on the tap, the combi boiler instantly heats the water as it flows through the unit, ensuring hot water whenever you want it.

Combi boilers run on natural gas, propane, or electricity and are super efficient, which is great news for homeowners who want to keep their energy bills in check. Plus, they’re compact and don’t take up much space, perfect for houses with limited room.

Not only do combi boilers handle your hot water and heating needs, but some models can even power underfloor heating systems, making them a versatile choice for homeowners.

How do combi boilers work?

A combi boiler does its magic by heating water straight from the mains as it flows through the unit. So when you turn on a hot water tap or hop into the shower, the combi boiler senses the water movement and gets to work.

Inside the boiler, natural gas or propane gets burned to heat up a special gadget called a heat exchanger. This heat exchanger takes that hotness and passes it on to the water as it goes through, making it nice and warm. The result? Instant hot water whenever you need it.

When it comes to heating your home, the combi boiler kicks in with the help of a circulation pump. It pumps that hot water through your radiators or even underfloor heating, ensuring your place stays cosy.

Combi boilers are all about efficiency. Some newer models have clever controls and burners that can adjust the heat output according to your needs, which means less energy waste and lower bills for you.

Types of combi boiler

When it comes to combi boilers, there are two main types: gas and electric. Let’s take a quick look at each:

Gas combi boilers: Gas combi boilers are the most common and run on natural gas. They’re highly efficient and provide heating and hot water on demand. If your home has access to mains gas, a gas combi boiler is usually a reliable choice.

Electric combi boilers: Electric combi boilers are less prevalent and operate on electricity instead of gas. They’re typically smaller in size and can be a viable option for homes without gas connections. However, it’s important to note that electric combi boilers may be more expensive to run because electricity generally costs more than gas.

So, these are the two main types of combi boilers to consider. Of course, whether you go with gas or electric depends on your home’s setup and your budget.

Advantages of a combi boiler

Combi boilers come with a range of advantages that make them a great choice:

  • Space-saving: One major perk of a combi boiler is that it doesn’t require a separate hot water tank. This makes it a space-saving solution, especially for homes with limited room.
  • Energy-efficient: Combi boilers are highly efficient in their energy usage. Many models have advanced controls and modulating burners, which adjust the heat output according to the demand. This helps to reduce energy consumption and save on costs.
  • Instant hot water: Hot water is available on demand with a combi boiler. You don’t have to wait for a tank to heat up, ensuring that you always have hot water whenever you need it, whether it’s for showering or other household tasks.
  • Cost-effective: Combi boilers are cost-effective in several ways. Since they don’t require a separate hot water tank or complex piping system, the installation and maintenance costs are generally lower. This can save you money in the long run.
  • Versatility: Some combi boilers go the extra mile. They can power underfloor heating systems, adding a versatile feature to your heating setup.
Repairing Work On Combi Boiler

Disadvantages of a combi boiler

While combi boilers come with many advantages, there are also a few drawbacks to keep in mind:

  • Limited hot water supply: Combi boilers provide hot water on the spot, but they limit how much they can handle at once. The hot water supply might not keep up if you’re using multiple taps or showers simultaneously.
  • Pressure problems: Combi boilers rely on the water pressure from the mains to deliver hot water. If your water pressure is low, you might face issues like reduced water flow and temperature fluctuations.
  • No backup system: If a combi boiler decides to take a break and stops working, you won’t have a backup plan. Since it’s an all-in-one unit, you might find yourself in a pickle until you get it fixed.
  • Tricky installation: Installing a combi boiler can be more challenging than a traditional heating system. It requires careful consideration of your place’s water pressure, flow rate, and the right size and output. It’s not a simple DIY project.
  • Maintenance demands: Combi boilers need regular maintenance to keep them humming smoothly and safely. This includes cleaning the heat exchanger, checking for leaks, and servicing the unit once a year.

Choosing the right combi boiler for your home

Choosing the perfect combi boiler for your home can feel like a big task, but fear not! Here are some important factors to consider:

  • Size and output: The boiler’s size and output should match your home’s needs and your hot water and heating requirements. Seek guidance from a professional installer to determine the right size and output for your specific situation.
  • Energy efficiency: Look for a combi boiler with a high energy efficiency rating. This will help you save on energy costs in the long run, so it’s a wise investment.
  • Controls: Some combi boilers offer advanced controls like programmable thermostats. These nifty features allow you to fine-tune your settings, save energy, and enhance your comfort levels.
  • Brand and reliability: Opt for a reputable brand with a proven track record of reliability and good customer support. It’s worth paying a bit more for peace of mind and knowing that your boiler will serve you well for years to come.
  • Installation and maintenance: Consider the installation and maintenance requirements of the boiler. These factors can impact the overall cost and convenience of owning a combi boiler. Make sure to factor in any additional expenses and the availability of professional maintenance services.
  • Cost: Combi boilers come in various price ranges. While staying within your budget is important, remember that the cheapest option may not always be the best. Look for a boiler that offers good value for money and meets your needs effectively.

Maintaining your combi boiler

Keeping your combi boiler in tip-top shape is crucial for its efficiency and reliability. Here are some simple steps to maintain your combi boiler:

  • Annual service: Get a pro to service your boiler once a year. They’ll clean it up, inspect the parts, and check if everything’s running smoothly and safely.
  • Bleed radiators: If your radiators aren’t warming up as they should, they might need a good bleeding. This releases trapped air, making your heating system work better and preventing boiler troubles.
  • Check pressure: Keep an eye on the pressure gauge. Make sure it stays within the recommended range. Low pressure can shut down the boiler, while high pressure can cause damage. So, keep it in the sweet spot.
  • Clear vents: Don’t block or cover the air vents on your boiler or in your home. Blocked vents can lead to overheating or boiler shutdowns. Keep them clear for smooth operation.
  • Regular cleaning: Give your boiler’s exterior a wipe-down regularly. Dust and debris can gather, affecting its efficiency and risking breakdowns. Keep it clean and happy.
  • Follow the manual: Stick to the manufacturer’s instructions for maintenance tasks and service intervals. They know their stuff, so it’s wise to follow their lead.


What is a combi boiler, and how does it work?

A combi boiler is a compact heating and hot water system that provides both space heating and hot water on demand. It works by heating cold water from the mains as it passes through a heat exchanger, delivering hot water to taps and showers without needing a separate tank or cylinder.

Are combi boilers energy efficient?

Combi boilers are highly energy-efficient because they only heat the water you need when needed, eliminating the need for a separate hot water tank. This means they can be more cost-effective than traditional boilers and can help reduce energy bills and carbon emissions.

How long do combi boilers last?

The lifespan of a combi boiler can vary depending on the quality of the unit and how well it is maintained. On average, a combi boiler can last anywhere from 10 to 15 years.