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Combination Boilers / System Boilers / Conventional Boilers / Oil Fired Boilers

What Is A System Boiler?


How do I decide which type of condensing boiler best suits my needs?

There are 3 different types of high-efficiency condensing boiler:

  • Combi
  • Regular (a regular boiler is often also referred to as a “traditional” or “conventional” boiler.)
  • System

Each type delivers all the benefits of high-efficiency technology, but which one you choose will depend on several factors, including your property, your lifestyle and the professional advice of your CORGI (gas) or OFTEC (oil) registered installer.

What is a system boiler?

Top Left image is an example of a central heating and hot water system layout using a system boiler with a pressure hot water cylinder.

Bottom Left image is an example of a central heating and hot water system layout using a system boiler with an unvented hot water cylinder

Unlike a combi, both a system boiler and a regular (conventional) boiler work on the principle of stored hot water - but a system boiler differs from a regular boiler in some important respects.

Firstly, many of the major individual components of the heating and hot water system are built in, which means that installation is quicker, neater, easier and more efficient.

Secondly, the hot water is pumped from the boiler through the system to the radiators and hot water cylinder, resulting in a fast response and more economical running costs. The system boiler removes the need for a feed and expansion cistern.

Here are a few examples and guidelines to think about and help you identify the type of condensing boiler most likely suited to your needs.

Consideration Most suitable boiler
You want to use your loft space for a room conversion or other purpose COMBI
You live in a flat or bungalow (i.e. have very little or no roof space) COMBI
Your home has more than 2 bathrooms REGULAR OR SYSTEM
Your main water pressure is low REGULAR OR SYSTEM
You want to replace an old boiler to improve an existing conventional central heating system REGULAR, SYSTEM or COMBI
There is a need to have hot water available on tap without waiting for it to heat up. COMBI


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