What is a Combi Boiler?

What is a combi boiler?

A combination boiler or combi boiler is a gas central heating boiler that is also an instantaneous water heater.

A combi boiler is an ingenious space-saving idea, and an increasingly popular choice in UK homes. In fact, combi boilers now account for well over half of all the new domestic boilers installed in Britain every year.

A combi boiler is both a high-efficiency water heater and a central heating boiler, combined (hence the name) within one compact unit. Therefore, no separate hot water cylinder is required, offering space saving within the property.

Further benefits of a combi boiler includes hot water being delivered through your taps or shower at mains pressure. So you can enjoy powerful showering* without the need for a pump.

Another combi boiler benefit is that it can generally save you money on installation time and costs, since no tank in the roof space means less pipe work and a shorter installation time.

How does it work?

A Combi boilers works the same as a standard boiler by burning gas and producing heat. This heat is then used to warm the water passing through the boiler using a heat exchanger. With a standard boiler that water would then flow through your radiators or hot-water cylinder. A Combi boiler works differently by having a second heat exchanger that transfers heat from the main heat exchanager to the mains cold water passing through the boiler when a hot tap is tuned on.

Why a combi boiler?

Lower energy bills
With efficiency of 90%, for every £1 you spend on energy, only 10p is wasted. When you consider that some of the older non-condensing boilers only reached 55% efficiency, it represents a significant saving. For example, when replacing a boiler with less than 70% efficiency with one of the most efficient condensing units you could save up to £305 on your heating bills in one year.*

Compact size 
Imagine finally being able to get rid of that bulky water tank and / or storage cylinder that sits in your attic or airing cupboard. A Combi boiler is just one simple unit and some are small enough to be concealed in a kitchen cupboard. This is particularly great news for those living in small homes or flats.

High energy efficiency
A Combi boiler is typically over 90% efficient which is the highest level of efficiency on the market, helping you to reduce your carbon footprint.

Hot water on demand
There is no need to store hot water which means less energy used and none of that inconvenient waiting around for a hot water tank to refill.

Mains pressure
A Combi boiler takes its water supply directly from the mains which can often mean you get a much stronger pressure of hot water through your taps and showers.

Easy to install
As there’s no need for multiple elements a Combi boiler is usually simple to install and, unlike system or conventional boilers, it can be fitted anywhere in the home.

What to consider

Make sure you have an adequate supply of water coming from the mains. If the mains pressure is weak or inconsistent, your showers and taps will be too. This single flow of water is also a problem if you have several showers, baths and sinks that need to be used simultaneously as the flow will try to split between them all and weaken as a result.

If you have a higher demand for hot water then a high efficiency, condensing system or conventional boiler may be the answer.

All condensing boilers require a condensing pipe to drain the condensed vapour and dispose of it down a drain. If the installer can’t add a pipe where the existing boiler is positioned then it may need to be relocated; this may add to the cost of installation.

Who make combi boilers?

The main manufactures of combi boilers in order of recommondation are:

Vaillant, Worcester, Viessmann, Ideal, Baxi, Vokera, Potterton, Glowworm, Biasi, Ferroli.

Cons of combi boilers

Despite the popularity of combi boilers, there are several issues that you should bear in mind when considering replacing your boiler.

The disadvantages of combi boilers include:

Dependence on Mains Pressure

To ensure that your combi boiler is working properly, you need good mains pressure. If you are having a new boiler fitted, you should check what the mains pressure in your area is before you go ahead with the installation.

Limited Use

With a combi boiler it is not possible to run more than one shower or bath at a time, or to turn on the hot tap while showering. This may be an issue if you live in a large house with a number of bathrooms and en suites, or with lots of people.

No Immersion Heater

As there is no water tank, if your combi boiler breaks down then you will be left without hot water as well as central heating (unless you install an electric shower).

No Power Shower

You can’t have a power shower with a combi boiler, as the water pressure is set by the pressure level at the water mains.