What is a combi boiler?

Suited to small to medium homes with less hot water demand, combi boilers can provide heating and hot water on demand, directly from your mains supply.

Choose the right boiler for you

Choosing a new boiler can be confusing.  There are a variety of boiler types  and models available on the market, but increasingly combi boilers are the recommended boiler for your home.

Is a combi boiler right for me?

Combination (or combi) boilers are the most popular type of boiler in the UK as they are compact, efficient and produce hot water on demand. Unlike system and regular boilers, combi boilers don’t have a cold water storage tank or a hot water cylinder, making them ideal for small to medium homes where space is limited.

How does a combi boiler work?

Combination boilers provide both central heating and hot water. Both systems can’t work at the same time, so the central heating temporarily turns off when you’re using the hot water. This all happens automatically and is usually something you don't even notice.

When the heating turns on, the water in your radiators travels back to the boiler, is reheated, and then sent back into the central heating system. The boiler stops when the desired temperature is reached (around 18-20 degrees centigrade) and when it gets a signal from the thermostat that the temperature has fallen, it fires up again. 

How does a combi boiler heat water?

As soon as a tap or shower is turned on, cold water passes from the mains to your boiler where a heat exchanger heats it up almost immediately and then it’s sent to where it is needed. When the hot water is turned off, the control valve in your boiler allows the water in your central heating system to flow back to the boiler. This allows you to use energy effectively and efficiently for all your heating needs.

The benefits of choosing a combination boiler


Most modern combi boilers have an efficiency rating above 90% because they’re condensing boilers, meaning they take and re-use the energy from waste gases which would otherwise be lost.

Compact size

Most combi boilers fit between kitchen cupboards - some will even fit in a standard kitchen cupboard. No water tank means less installation time. Many can be fitted in under a day.

How to keep a combi boiler working efficiently

Whilst combi boilers are generally efficient, there are a few other things you can do so it’s performing at its best.

Installing a smart thermostat will enable you to manage your boiler remotely via an app. You can adjust your heating automatically based on the time of day or turn it on and off remotely from your phone, helping you to be more efficient and save on energy bills.

Regular servicing will help to keep your boiler working well and we'd recommended booking a boiler service once a year. If you choose to buy a boiler from us you can add our exclusive boiler plan to cover the cost of boiler servicing for three years. You can also get up to a 10-year guarantee with us, which will cover you for almost any problem with your boiler at no extra cost.

How much is a combi boiler?

The cost of a combi boiler depends on the size you need and the brand you choose. Our prices for a new combi start at £1,995 if you buy your boiler online. They’re affordable, energy-efficient and don't take up a lot of space - an ideal choice for small to medium-sized homes. 

If you want more advice, book a video survey with our heating experts to help you find the right combi boiler for your home. To find out more, read our article about how much a boiler costs.