What is a Combi Boiler?

A combi boiler is a type of boiler that provides both hot water and central heating in the same system. The name “combi” comes from the original term “combination boilers” as their design is to combine all the components of a traditional central heating system into one compact unit.

In this guide, we will take you through how a combi boiler works, how it differs from other boilers and why you should consider getting one for your home.

How does a combi boiler work?

Combi boilers work by heating water directly from the mains supply, eliminating the need for an external hot water cylinder or cold-water storage tank.

When you require heating or hot water, the gas burner inside of the combi boiler ignites. The heat from the flame is transferred through the main heat exchanger to the primary circuit. From there, the heat is moved directly to either the radiators or to your taps, via a plate heat exchanger.

A pre-heat system is part of many modern combi boilers to deliver hot water instantly and efficiently. This allows the boiler to store a small amount of water which can be drawn from the boiler. The water is held and maintained at your desired temperature throughout the day, ready to be sent to the hot water tap when required.

When your thermostat notifies the boiler that the temperature has dropped below a certain point, the boiler will send hot water into the central heating system until the temperature goes back above the level on the thermostat, at which point the boiler will modulate and stay at that level.

What is the difference between a combi boiler and a regular boiler?

A combi boiler differs from a regular boiler in the way they operate. Whilst a regular boiler has a separate hot water cylinder and cold-water storage tank, a combi boiler provides both through one combined unit.

Advantages of a combi boiler

Combi boilers are popular with many homeowners because of their various benefits. These include:

Speed

The speed at which combi boilers can provide hot water is one of the main advantages that set them apart from alternatives. By utilising preheating technology that isn’t available in alternatives like system boilers and regular boilers, combi boilers heat water when it is required. With a combi boiler, you know you will get a continuous supply of hot water.

Size

Without the need for an external cylinder, combi boilers can be very compact. Their size gives homeowners back some storage space as they can be placed in a small airing cupboard.

Savings

The easy installation and the fact that combi boilers are a single unit means that they’re a much more cost-effective option than larger, conventional systems. They also require less upkeep as they are not hugely complex systems and only require an annual service on the boiler and no additional annual service on an unvented cylinder.

Are combi boilers gas or electric?

Combi boilers are available in multiple different fuel types; gas, electricity, oil and LPG (Liquified Petroleum Gas). Navien combi boilers work on gas condensing technology for high energy efficiency.

Where is the best location for a combi boiler?

The best location for a combi boiler is as close to the gas pipes as possible, on an external wall to allow the boiler to take in and vent out air, the same as any type of boiler. This is due to safety as the shorter an exhaust on a boiler, the less risk of any leaks.

Having a boiler closest to where your gas pipes enter your home will also provide a cost saving. This is because it reduces the need for extended gas pipework and expensive exhaust ducting to and from your combi boiler.

Your installer will survey your home and find the best place for your boiler.

What is the difference between a combi boiler and a Combi Crossover?

The Combi Crossover is the next generation of high-performance boilers. It combines the power and performance of a system boiler with the advantages of a combi boiler without a cylinder. This eliminates slow heat-up times and low water flow rates.

Powered by the innovative pre-heating NCB ON technology, the Combi Crossover puts hot water first, removing the fluctuation between hot and cold to provide quality, consistent and efficient hot water.

Can a combi boiler run multiple showers at once?

While standard combi boilers cannot provide hot water to multiple showers at once, the NCB700 ON Combi Crossover is powerful enough to deliver hot water to three bathrooms simultaneously.

Is a combi boiler the right choice for my home?

The everyday combi boiler can supply single hot water outlets, but it suffers when serving multiple outlets simultaneously. We recommend making sure that the combi boiler you are considering will be able to efficiently serve your home, as different boilers are designed for homes of specific sizes.

It’s not only the size of your home that can determine whether your home is right for a combi boiler. Combi boilers take water directly from the mains so you will need to have good mains pressure because the pressure drops as more outlets are used at once. If you have low water pressure, you may be required to add a mains booster or accumulator to use a combi boiler in your home.

If you’re unsure that a combi boiler is the right choice for you, find out how to choose the right boiler for your home in our guide.

How long do combi boilers last?

Combi boilers typically last 10-15 years, depending on the model and how regularly they are serviced.

Navien combi boilers and Combi Crossover boilers have a warranty of up to 12 years and have been engineered for reliable long-term performance.

You can find out more in our in-depth guide: how long do combi boilers last?

How much do combi boilers cost to install?

The price of a combi boiler will differ depending on the model and size and the type of property it is being installed in. You can use our handy find a boiler tool to discover the best Navien boiler for your home.

For more information on our range of combi boilers, get in touch or find a local installer today.