What is a System Boiler?

System BoilersA system boiler (also known as sealed system) heats your central heating system directly and produces hot water for your cylinder. The cylinder usually sits in an airing cupboard and there is no water tank.

A system boiler, just like a regular (conventional) boiler works on the principle of stored hot water. However, 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 into a system boiler, which means that installation is quicker, neater, easier and more efficient.

Secondly, the hot water is pumped from the system boiler through the heating 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


  • there’s no need for a tank in your loft.
  • you can get hot water from multiple taps at the same time.


  • you don’t get hot water instantly.
  • the hot water can run out and you’ll have to wait for it to reheat.
  • you need to find room for the cylinder somewhere.

Suitable for

  • Homes which need to have hot water in more than one place at the same time.