Should I Get a System Boiler?

Martyn Bridges from Worcester, Bosch Group takes a closer look at this central heating option
Worcester Bosch Group
by Worcester Bosch Group
1st October 2017

When it comes to choosing a gas boiler, there are three main options: regular (a traditional setup where a water storage tank feeds a hot water cylinder); combi (which sends hot water directly to the emitter without storing it in a cylinder); and system boilers.

Here, I’m focusing on system boilers and how you could benefit from this way of powering your central heating.

What is a system boiler?

This appliance can provide a full heating and domestic hot water (DHW) solution.

Much like a regular boiler, it works in conjunction with a storage cylinder, allowing several hot water outlets to be fed at the same time – which makes a system model an ideal choice for larger homes with multiple bathrooms.

There are two options for the cylinder: either a mains-pressure version, or a low-pressure one gravity-fed by a cold water cistern in the loft.

Worcester system boiler used for central heating

The Greenstar I System boiler is part of Worcester Bosch’s latest generation of Which? Best Buy boilers

But there are several important differences between a system boiler and regular appliance.

Firstly, with a system boiler the major individual components (such as the expansion vessel) are built-in, meaning installation is quicker and less costly.

Secondly, the hot water is pumped from the boiler though the system to the radiators and hot water cylinder, resulting in a fast response time and more economical running costs.

Worcester boiler
Worcester system boiler

Key considerations

When putting a new heating system in place, the arrangement as a whole – from the boiler output through to the radiator and hot water cylinder size, as well as the reheat time – needs to be taken into consideration.

All components within this must be correctly measured to suit the demand as efficiently and cost-effectively as possible.

Gas is the most cost-effective fuel option if you have suitable access from your site, otherwise there are oil-fired boilers that will offer a similar outcome.

System boiler Worcester Bosch

System boilers can provide full heating and domestic hot water

For houses with multiple bathrooms, a stored water setup can cater for demand comfortably.

You can install a system boiler with a vented system. But if you wish to boost pressure, consider an unvented, mains-fed cylinder as it will ensure you have the water pressure you need to run the shower and bath at the same time.

These come in a range of sizes from 90 litres up to 300 litres to cater for differing hot water needs. It’s worth noting how quickly you would like the water to reheat to make sure you have sufficient supply when you need it.

System boilers are compatible with renewable technology so you can enjoy the benefits of environmentally friendly heating and hot water plus further cost savings.

Solar thermal panels could also help support the supply of domestic hot water, so if you think you might go for this option, consider fitting a suitable twin coil cylinder from the outset.

central heating system boiler

The price of your system boiler will vary depending on what type of installation you require

System boiler costs

The average cost to install a system boiler is around £900, but this can vary depending on the house type, location and the installation work required.

Your heating installer will be able to advise if a system boiler is suitable for your house and provide a quote.

Martyn Bridges began his career as a plumbing and heating apprentice and has a strong technical knowledge of boilers and renewable heating systems. He is now the director of marketing and technical support at Worcester, Bosch Group. For further information about Worcester, Bosch Group call 0330 123 9339 or visit

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