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What is a system boiler?

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For larger homes with multiple bathrooms, a system boiler could be the perfect fit. It saves space (no water tank needed, just a hot water cylinder!) and can run hot water to several bathrooms at a time, making it a great choice for households with large, busy families. They can help you save on running costs and installation, while they’re also a great way of improving your home’s energy efficiency.

How Does a System Boiler Work?

The expansion vessel and pump are in-built components of the system boiler, making it easy to install, easy to maintain, and more efficient than many other boilers that are on the market. In addition, the inbuilt components help to make it a more compact option, which is perfect for properties where space is at a premium. Hot water is pumped from the boiler into your home’s radiators, reducing your running costs and ensuring a fast response time for your heating.

Although compact, their ability to run hot water to multiple taps and showers simultaneously makes them a great choice for large households with higher water demands. Since there’s no need for a water tank, a system boiler is probably the best choice if you’re planning on carrying out a loft conversion.

Why choosing the right system boiler is important

Choosing the wrong boiler can get pretty ugly especially when it comes to trying to save on energy bills or guaranteeing the correct flow of hot water. The wrong type of boiler will lead to extortionately high energy bills and long delays in hot water reaching your home’s outlets.

System boilers can heat homes with up to 7+ bedrooms, so the sky is almost the limit for this type of boiler. Unlike combi boilers, system boilers heat water to then be stored in a hot water cylinder for later use. This is great for homes that require a lot of hot water for several outlets.

How do I know if a system boiler is right for my home?

There are a few ways to tell if a system boiler is suitable for your home. The most obvious way to tell is the current layout of your central heating system. If your home only has a boiler, and a pressurised hot water cylinder like a megaflow installed but doesn’t have a loft-installed tank, your current boiler is a system boiler. Like-for-like system boiler swaps tend to be a lot easier for engineers.

If you haven’t got a system boiler installed, or still unsure about which size system boiler you’ll need, there are a few factors you’ll need to consider before you choose a boiler (don’t worry, we can help you find the boiler you’re looking for). Your household’s demand for hot water, which is essentially how much hot water you're likely to use, will decide the size of the boiler you need installed. A system boiler will pre-heat water and store the heated water within a cylinder; therefore you can determine exactly the output you’ll need based on the demand for hot water and the size of your property.

Advantages of a System Boiler

The chief advantage of gas system boilers is their ability to supply multiple bathrooms and faucets with hot water at the same time. This is indispensable for large families and is part of the reason why system boilers are one of the most popular types around. Other pros include:

  • Hot water always available
  • Energy-efficient and environmentally friendly
  • No need for a cold water tank
  • Flow rates tend to be high and at mains pressure
  • Affordable running costs
  • Save money on utilities, particularly if you’re replacing an old boiler
  • Can be used with solar thermal systems

Disadvantages of a System Boiler

However, there are a few disadvantages when it comes to this model type:

  • Hot water may need to be reheated
  • May need to pre-program your boiler if you want hot water at a specific time
  • Requires a little extra space for the hot water cylinder
  • Cylinder size may dictate how much water you’re able to use
  • No need for a cistern in the loft
  • May need insulation in order to stop heat and energy loss

Energy Efficiency

Since 2005, all new boilers installed in UK homes must be condensing boilers. If you install a system boiler, it’s going to be a condensing one. These boilers are energy efficient, extracting over 90% of the heat from the fuel that they burn, and as such, they’re highly cost-effective. Essentially, heat is extracted from flue gases and then recycled back into the heating system. This makes them a green and environmentally-friendly choice.

In addition, system boilers have a range of environmental benefits of their own. They can be used in conjunction with solar thermal systems, which can help you to reduce your energy bills and lower your carbon footprint.

System Boiler Alternatives

It’s important to choose the boiler that’s right for your home. Although system boilers remain a popular choice throughout the UK, there are some alternatives:

Combi boilers are a cost-effective home heating solution. They don’t need a hot water cylinder or tank – they’re a sealed system – which saves money and space, while their energy efficiency makes them an environmentally responsible choice. They control both hot water and central heating, delivering water directly from the mains. Combi boilers are strong choices for smaller homes, although if you have multiple bathrooms they may not be the most effective choice since they tend to struggle to produce the amount of hot water necessary for larger families and/or homes.

Conventional boilers, which are also known as regular boilers, need both a water tank and a cylinder. They are a better choice for homes which have traditional heating systems, as any changes to pipework are likely to be minimal. They can provide large volumes of hot water and serve multiple bathrooms at the same time, however, one potential drawback of these boilers is that they may need time to heat up your hot water.

Head over to our comprehensive boiler guide if you’d like to know more about alternatives to system boilers.