10th May, 2022

What Is A System Boiler?

The best boiler for your home will be one that can meet the demands for hot water and central heating within the household.

What Is A System Boiler?

A system boiler is one of the best for homes with a high demand for hot water because they store hot water in a separate cylinder, which gives you constant access.

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There are lots of different kinds of boilers and boiler systems out there which can make it hard for you to find the best one for your home. With the right engineer on your side, you can find an efficient boiler system that will provide hot water and central heating on demand, at a rate that is suitable for your household.

For many homes, a system boiler can be the best option, and we have written this guide to help you figure out whether this is the case for you. We are going to discuss what a system boiler is, how much they cost, as well as the pros and cons of this kind of boiler.

What Is A System Boiler?

First things first, we need to talk about what a system boiler is. This is one of the three main kinds of boiler systems that are available in the United Kingdom.

A system boiler works by directly providing heat to your central heating and hot water system through a storage cylinder. This kind of boiler works similarly to a conventional or standard boiler, as both types need to store hot water that can be used throughout the house. However, there are some key differences between the two.

Unlike regular boilers, a system boiler takes water directly from the system in your home.

This makes them a more compact system than regular boilers, while still being able to provide a high volume of hot water, making them highly versatile.

How Does A System Boiler Work?

To help you decide whether a system boiler is the right option for your home, let us take a look at how they work.

Some kinds of boiler, such as an oil boiler, require large external parts in order to provide heating and hot water. For an oil boiler, for example, an oil tank also needs to be installed along with the boiler unit to provide fuel.

However, with a system boiler, almost everything is built inside of the unit. The only external part of this kind of boiler is the hot water cylinder which holds hot water.

System boilers work by taking hot water directly from the system that is already in your home, as they are connected directly to the mains. As they have a direct connection, there is no need for a hot water tank which would have to be installed into the attic as with regular boilers.

Instead, the cylinder is a smaller unit and is used by system boilers for both hot water and central heating. These kinds of boilers can provide heating and hot water on demand for as long as the hot water cylinder is full.

The hot water cylinder does need to be refilled from time to time.

Is A System Boiler The Best Kind?

There are three main kinds of boiler systems available – system boilers, combi boilers, and regular boilers.

To help you determine whether a system boiler is the right choice for you, we need to make some comparisons between the different kinds of boilers that are available. The best kind of boiler system will be one that can provide a good level of hot water and central heating based on the demand within your household.

System Vs. Combi Boilers

Combi boilers, also known as combination boilers, combine both hot water and central heating into one unit.

As system boilers rely on a hot water cylinder, which is external, they can provide a higher volume of hot water than combi boilers. As hot water is kept on standby in an external cylinder with system boilers, they can provide more hot water than combi boilers that keep everything in one unit.

Combi boilers are great for homes with limited space, as they are compact units that have everything contained in one, whereas system boilers require external cylinders as well as the boiler unit. But this does not mean that combi boilers are free from limitations.

Without an external cylinder for hot water, which system boilers rely on, combi boilers cannot provide as much of a high demand for hot water. This can cause issues in large homes with multiple bathrooms or households that are home to a lot of people, all of which have their own demands for hot water. 

If you live in a large home with multiple bathrooms, your best bet is a system boiler instead of a combi boiler.

System Vs. Regular Boilers

Regular boilers are known by several different names, including conventional, heat-only, or open-vetted. These are the terms to keep in mind when shopping for regular boilers, as each brand uses slightly different variations on the name.

These kinds of boilers are traditional systems, and they are usually found in older homes, so many people in the United Kingdom might have some experience with a regular boiler system.

Unlike both system and combi boilers, regular boilers are not directly connected to the water mains of your property and so do not get the water this way. Instead, for regular boilers to get water for the heating system feeder an expansion tanks also need to be installed. These are usually installed into the attic of a property.

For regular boilers to work, the feeder unit fills with cold water which it gets from the mains. This water then flows down to the boiler, with the help of gravity, as the expansion vessel keeps the level of water consistent.

An expansion vessel must also be installed along with a regular boiler and feeder as the water expands when it is heated.

The pipework that is needed for regular boilers to be installed makes the process complicated. In most cases, regular boilers are only recommended in a like-for-like replacement which means that if you already have a regular system, then getting a new regular boiler is a good idea.

A system boiler is more straightforward to install, which can make it a better option for most homes. There is less pipework required, and the installation process will be quicker, which can be a great advantage for most properties.

Pros Of System Boilers

System boilers combine the best parts of a regular boiler and combi boiler, giving you reliable hot water and central heating on demand.

Like a combi, system boilers get hot water directly from the mains supply, which can make them better for smaller homes as it eradicates the need for a hot water tank in the attic like traditional systems. With system boilers, hot water is stored in a separate cylinder to meet a higher demand which is why they are a great option for larger homes or those with multiple bathrooms.

There are various pros of system boilers that all homeowners should be aware of, as this can help them decide whether this is the right choice for their property.

System boilers take on the best parts of a combi boiler and a regular boiler such as:

Easy Installation

System boilers offer a simpler installation process than other kinds of boilers because they do not rely on complex pipework as regular boilers do.

In a system boiler, most of the heating and hot water compartments are installed into the unit, and the only separate part of the boiler is the hot water cylinder. The unit for this kind of boiler is compact, which makes it versatile, and is easy to install into even small spaces such as an airing cupboard.

High Hot Water Demand

System boilers are perfect for large homes or those with multiple bathrooms as they can provide a high hot water level on demand. As they rely on a separate hot water cylinder, the hot water levels provided by system boilers are higher than traditional systems making them the best for larger properties.

With the separate hot water cylinder, multiple taps can be turned on at once allowing multiple people to get bathed, take a shower, or wash the dishes at the same time without limiting the hot water access in the house.

Strong Water Pressure

Likewise, as system boilers rely on a separate hot water cylinder, they can provide a stronger water pressure than other systems.

The water used by system boilers comes directly from the mains, as opposed to a separate tank in the loft like traditional systems, the water that comes out of your taps or showers will be at a higher pressure.

Economical Running Costs

System boilers have a pump, which allows them to operate faster and run more economically than other models.

Space Saving

As system boilers do not require a separate tank or a feed, they are space-saving.

The only separate part of a system boiler is the hot water cylinder which is compact. System boilers are great for properties without a loft.


System boilers can be more efficient than other models because of the high water demand they provide. Another great factor of these boilers is the fact they can also be combined with solar-powered panels, making your home more environmentally-friendly.

The hot water cylinder can be paired with solar power to keep the temperature high, and this is a great option if you are concerned about your impact on the environment.

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