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Condensing Gas System Boilers

What is a system boiler and how does it differ from other condensing boilers?

With so many different types of boiler it can be a minefield to know which one is best suited to your particular circumstance, many variables come into play when choosing a boiler and should only be done by a competent specifier and installer. Be sure to visit our Boiler Buying Guide for more information on choosing a boiler.

System Boiler

What is a System Boiler?

A system boiler is similar in some respects to a regular boiler in that they both work on the principle of stored hot water. However, they differ in one important respect in that a system boiler does not require a feed and expansion tank. This frees up valuable space in the loft and results in a cheaper, neater and more efficient installation.

Unlike a combi boiler you still require a hot water tank, usually within the airing cupboard so you can still benefit from a full tank of hot water and a useful area for drying towels.

Another advantage of a system boiler over a regular type is that hot water is pumped directly from the boiler around the radiator system and hot water tank, this results in a faster response time and lower running costs.

A system boiler tends to be larger than a regular boiler as it contains the expansion vessel, filling loop and pump, however, many advantages including simple installation as most of it is pre-plumbed, pre-wired and tested prior to delivery.


  • Inexpensive to run
  • Reliable
  • No tanks in loft, no risk of leakage and more space


  • Physical boiler takes up more space
  • Usually more expensive to buy than a regular boiler

When Should a System Boiler be Used?

It’s important to seek professional advice on which boiler is best suited to your requirements, in general a system boiler is a good choice if you have no room in the loft for an expansion tank and have a large family wishing to take hot water from several different sources at once, but remember, take advice form a professional and arrange for more than just one quote.


System Boiler Installers