What Is A Combi Boiler?

Combi boilers, also known as combination boilers, can provide both central heating and hot water for your home as and when you need it. In addition to being highly efficient and more compact than most other central heating systems, combi boilers are the most commonly installed type of boiler in homes across the UK.

Why Are Combi Boilers the Most Popular Boiler Type?

Although not suitable for all properties, combi boilers account for more than half of all new domestic boilers installed in the UK every year. They’re popular because they provide heating and hot water from a single unit and are often smaller than most other types of boilers. 

Another reason why combi boilers are the most common type of boiler installed is they can supply hot water on demand without the need for a separate storage tank or cylinder, making them ideal for homes with limited space. What’s more, modern combi boilers tend to be more efficient than other boiler types, with some being up to 98% efficient.

How Does A Combi Boiler Work?

A combi boiler takes water directly from the mains water supply and heats it whenever you need hot water. So, when you switch on your thermostat or turn on a hot tap, the combi boiler acknowledges that you need hot water and then starts to heat water from the mains. 

The advantage of a combi boiler over other boiler types is that it can provide hot water on demand, meaning you always have fast access to hot water and central heating and never have to store hot water in a tank.  

Is A Combi Boiler Suitable for Your Home?

Combi boilers rely on the pressure from the mains to deliver a good water flow rate. If your mains water pressure is low or insufficient, a combi boiler will not be suitable for your home as it will struggle to deliver anything other than a trickle of hot water. 

A combi boiler is ideal for most homes with one or two bathrooms, but it doesn’t cope well when two showers or baths are running at the same time. Combi boilers struggle to meet high demands for hot water, so you will notice a dramatic reduction in water pressure when multiple hot water taps are in use. 

What Are Your Other Boiler Options?

The three most common types of boilers include combi boilers, system boilers and heat only boilers. If you’re still unsure whether a combi boiler is suitable, you can ask a Gas Safe registered heating engineer to help you choose the correct type of boiler for your home based on your heating and hot water needs. 

Let’s take a look at the other two main boiler options. 

System Boilers

If you have a high demand for hot water and limited loft space, a system boiler might be the ideal option. Unlike a combi boiler that heats water on demand, system boilers use a separate hot water storage cylinder to store water for later use. A system boiler will provide both heating and hot water, but it’s not connected to the cold mains and therefore needs to be installed alongside a hot water storage cylinder. 

As system boilers require a cylinder, they take up more space than combi boilers. However, system boilers can store hot water and meet high demands for hot water, making them suitable for larger homes and properties with multiple bathrooms. Just be aware that once all the hot water in the cylinder has been used, you have to wait for it to fill up again before you can use more hot water. 

Heat Only Boilers

Heat only boilers, otherwise known as regular, conventional or open vent boilers, take up the most space as they require a separate hot water storage cylinder and a cold water storage tank in the loft. Like with a system boiler, heat only boilers use a cylinder to store hot water. That means, once the hot water is used up, you have to wait for the boiler to produce more hot water. 

A heat only boiler is best suited to homes with two or more bathrooms and where several hot water taps are often in use at the same time. So, unlike combi boilers, heat only boilers can cope with multiple taps or showers running at once.