Why Are Combi Boilers So Effective?

boiler servicing, energy efficient boilers, energy saving

If you get a new combi boiler today, one of the first things you should notice is the efficiency rating. In some boilers, this could be as high as 98%. And while a 98% efficiency rating seems too good to be true, you can expect the boiler to realistically work at an efficiency that is very close to this figure. Yes, this is the 21st century and modern innovations are striving towards perfection. A 98% energy rating for a combi boiler is absolutely realistic.

But what makes combi boilers so efficient? What special features do they have over conventional boilers with relatively lesser efficiency? The efficiency of combi boilers stems from how they work.
The name, combination boiler, alludes to the dual purpose of the device. It serves as a home heating device while also providing on-demand hot water, although it cannot perform both activities concurrently.

These dual operations are made possible thanks to the innovative features of this excellent device. In this article, we talk about these features and how they contribute to making combi boilers such an efficient device.

But before that, here’s how combi boilers work.

How Do Combi Boilers Work?

A combi boiler has two heat exchangers. One of them, known as the primary heat exchanger, is responsible for heating the water that goes into the radiators and flows through it to heat your home. The flow of this water is a continuous cycle and the water gets recycled to be used again. Because of this, the water is often dirty and you cannot drink or use it for anything.

The secondary heat exchanger, on the other hand, only heats up the water that flows into the taps in your home.

As noted above, the two heat exchangers cannot work at the same time. Once you turn on a hot water tap, the operations of the primary heat exchanger are put on hold. The heated water in the radiators is then diverted into the secondary heat exchanger, providing the heat for water in sealed pipes that then flow into your taps.

This is a really simplified explanation of the operation of combi boilers.

More on the Heat Exchangers

The two heat exchangers make it possible for you to get hot water on demand. As a result, there is no need for a storage tank. This is in stark contrast to conventional boilers that require storage tanks to store water.

Additionally, once you run out of water in the storage tanks, you have to wait for some time, usually up to 30 minutes, to have heated water again. This is not the case for combi heaters as they provide water instantaneously.

The implication of this is that there is little room for heat loss in the water from a combi heater. While water in the hot water cylinder of conventional boilers may go cold without proper insulation, you need not worry about that when it comes to combi boilers.

Other features of combi boilers responsible for their high efficiency include;

Compact Design

The portable design of combi boilers makes them important in homes where space is an issue. Conventional boilers need to store water, and the storage tanks take up a lot of space. Combi boilers however produce hot water on an on-demand basis. This means that hot water is only produced when you need it. This eliminated the need for a storage tank and helps to preserve space.

Simple Pipework

Simplicity and efficiency go hand-in-hand. The less complicated a system is, the more efficient it is. And so it is for combi boilers with their light pipework and relatively few parts which not only makes installation and maintenance straightforward but also ensure you get water quickly when you need it. This goes a long way in aiding its efficiency.

Adjustable, Temperature-Regulating Thermostat

Another feature of combi boilers that makes them so efficient is the thermostat. Most combi boilers have two thermostats – one for each heat exchanger. These thermostats go a long way in ensuring the energy efficiency of combi boilers.

With these thermostats, you can programme the boiler to your preferred temperature level. Once the temperature of your home – or water – gets to this level, the boiler automatically stops. This alone will save you hundreds of pounds in fuel costs in a year.


Combi boilers are the most popular type of boilers in the UK. And there’s no prize for guessing why. They’re compact, portable, and can provide unlimited hot water for you on-demand. Moreover, they’re easy to install and economical to maintain.

Combi boilers will continue to hold sway for the foreseeable future. And if you’re thinking of changing or installing a new boiler in your home, you can’t go wrong with a quality combi boiler such as  Viessmann Vitodens 100-w combi boiler