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A Comprehensive Guide to System Boilers in the UK 2023

System boilers are a popular choice for heating homes in the UK. They are known for their efficiency, reliability, and compact design. In this comprehensive guide, we will delve into all aspects of system boilers, from their definition to installation and maintenance.

A Comprehensive Guide to System Boilers in the UK 2023

What is a System Boiler?

A system boiler is a type of central heating unit that heats water from the mains and stores it in a cylinder. This stored hot water can then be distributed to taps and showers as needed, providing your home with heating and hot water.

Unlike conventional boilers that require a separate hot water tank, system boilers have all significant components built into one unit, making them more space-saving. They are also known as sealed system boilers because their primary circuit is closed, allowing for quicker heat-up times and higher efficiency.

Importance of Choosing the Right System Boiler:

Selecting the right system boiler for your home ensures efficient heating and hot water supply. An appropriately sized system boiler will not only save you money on energy bills but also provide adequate heating and hot water without any disruptions.

Understanding System Boilers:

How Do System Boilers Work?

Unlike conventional boilers, system boilers don’t require a cold-water storage tank in the attic. They instead draw water from the mains and heat it with an internal heat exchanger. After that, the heated water is pumped into the hot water cylinder for storage.

Benefits of System Boilers:

Aside from their space-saving design, there are several other benefits to choosing a system boiler for your home. These include:

  • Quick and easy installation: As all major components are built into one unit, system boilers can be installed relatively quickly and easily compared to conventional boilers.
  • Energy-efficient heating: With sealed primary circuits and high-efficiency pumps, system boilers can provide efficient heating while reducing energy consumption and costs.
  • Hot water on demand: With a hot water cylinder, you can have a ready supply of hot water at all times without waiting to heat up.
  • Suitable for larger homes: System boilers are ideal for larger homes with multiple bathrooms, as they can supply hot water to several outlets simultaneously.

System Boiler vs. Combi Boiler: Which Is Right for You?

While both system and combi boilers are popular choices for heating homes in the UK, there are some critical differences between the two.

System boilers, as discussed earlier, have a hot water cylinder that stores pre-heated water. This means they can supply hot water to multiple outlets simultaneously without a pressure drop. On the other hand, combi boilers heat water directly from the mains and do not require a separate hot water cylinder.

If you have limited space, a combi boiler may be a better option as it doesn’t require a hot water cylinder. However, if you have multiple bathrooms or high hot water demand, a system boiler may be more suitable.

System Boilers

Types of System Boilers:

Open Vent (Regular) System Boilers:

Open-vent system boilers, known as regular or conventional boilers, have an open-vented hot water cylinder and a cold-water storage tank in the loft. These are suitable for homes with traditional heating systems and low mains pressure.

Sealed System Boilers:

Sealed system boilers, as discussed earlier, have all major components built into one unit. They are best suited for modern homes with high primary pressure.

Heat Only vs. Heat and Hot Water System Boilers:

There are two main types of system boilers based on their function: heat only and heat and hot water. Heat-only system boilers only provide heating to your home, while a heat and hot water system boiler can also supply hot water to taps and showers.

System Boiler Components:

Boiler Unit:

This is the primary unit of a system boiler that includes the heat exchanger, pump, and controls.

Hot Water Cylinder:

The hot water cylinder stores pre-heated water for later use.

Expansion Vessel:

When heated, the expansion vessel allows water to expand, preventing pressure buildup in the heating system.


The pump is responsible for circulating hot water from the boiler to the hot water cylinder and radiators.


System boilers have various controls, including a thermostat, timer, and programmer, to control heating and hot water supply.

conventional boiler

System Boiler Installation:

Finding the Right Location:

System boilers should be installed in a well-ventilated area with enough space for maintenance and repairs.

Professional Installation Requirements:

A Gas Safe registered engineer should install system boilers to ensure safety and proper functioning.

Cost of System Boiler Installation:

The cost of system boiler installation varies depending on several factors, including the type and size of the boiler, the location, and the complexity of the building.

Maintenance and Repairs:

Regular Servicing:

To ensure your system boiler continues to operate efficiently, it is recommended to have it serviced annually by a qualified engineer.

Common Issues with System Boilers:

Some common issues that may arise with system boilers include low pressure, leaks, and faulty pumps or controls. It is crucial to address these issues promptly to avoid any disruptions in the heating and hot water supply.

Troubleshooting Tips:

Here are a few troubleshooting tips for standard system boiler problems:

  • Low Pressure: Check the pressure gauge on the boiler, and if it is below 1 bar, you may need to top up the pressure using the filling loop.
  • Leaks: If you notice any leaks, it is vital to call a professional engineer for repairs.
  • Faulty Controls: Check the batteries in your thermostat and replace them if necessary. If the issue persists, you may need to call an engineer for further diagnosis and repairs.

System Boiler Energy Efficiency:

A-Rated System Boilers:

A-rated system boilers are the most efficient and environmentally friendly options available in the UK. They have an efficiency rating of 90% or above, meaning they convert at least 90% of their fuel into heat.

Improving Energy Efficiency:

Some ways to improve the energy efficiency of your system boiler include:

  • I am installing a weather compensation control that adjusts heating based on outside temperatures.
  • We are insulating your hot water cylinder and pipes to reduce heat loss.
  • You are upgrading to a smart thermostat to control heating remotely and optimize energy usage.

Government Incentives and Grants:

The Renewable Heat Incentive (RHI) and Green Homes Grant are two grants and incentives offered by the UK government to promote energy-efficient home heating.

System Boiler Brands and Models:

Popular System Boiler Brands in the UK:

Some popular system boiler brands in the UK include Worcester Bosch, Viessmann, Vaillant, and Baxi.

Best-Selling System Boiler Models:

Best System Boiler Models for Different Needs:

Green Heating Initiatives in the UK:

Sustainable Heating Options:

As the UK government aims to reduce carbon emissions and promote sustainable living, there are various green heating options available, such as heat pumps, solar panels, and biomass boilers.

Advantages of a System Boiler in Green Homes:

System boilers can work with renewable energy sources, making them an ideal choice for green homes. They also have high-efficiency ratings, reducing energy waste and carbon emissions.


System boilers are a popular and efficient choice for home heating in the UK. They come with various benefits, such as compact design, high efficiency, and compatibility with renewable energy sources. It is important to have a professional installation and regular maintenance to ensure optimal performance and longevity of your system boiler.

System boilers are an excellent option for those looking to reduce their carbon footprint and save money on energy costs, especially with the increased emphasis on green initiatives. If you are considering upgrading your home heating system, a system boiler is the perfect choice for you. Happy heating! #systemboiler #UKheating #energyefficiency

What is a system boiler?

A system boiler is a heating system that provides both hot water and central heating to a home using a pressurized cylinder, pump, and controls.

Do I need to have my system boiler serviced regularly?

Yes, it is recommended to have your system boiler serviced annually by a qualified engineer to ensure efficient operation and identify any potential issues.

Can I install a system boiler myself?

No, it is crucial to have a Gas Safe registered engineer install your system boiler to ensure safety and proper functioning.

Are there any government incentives for using a system boiler in the UK?

Yes, the UK government offers various grants and incentives for energy-efficient home heating, such as the Renewable Heat Incentive (RHI) and Green Homes Grant.

What are some popular brands and models of system boilers in the UK?

Some popular brands include Worcester Bosch, Viessmann, Vaillant, and Baxi, with best-selling models including Worcester Bosch Greenstar 30i, Viessmann Vitodens 100-W, Vaillant ecoTEC Plus, and Baxi Megaflo.

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