What is a Combi Boiler?
A combination (or "combi") boiler is both a high-efficiency water heater and a central heating boiler in a single compact unit. Combi boilers heat water directly from the mains when you turn on a tap, meaning you don't need a hot water storage cylinder or a cold water storage tank in the roof space.
What is a System Boiler?
System boilers require a cylinder for storing hot water, but the major heating and hot water system components are built into the boiler itself, making it quicker and easier to install than a regular (conventional) boiler. They don't need a tank in the loft, though.
Which One Do You Need?
If you have a smaller home with one bathroom and limited loft space, a combi boiler is usually the best choice. It provides instant hot water and takes up minimal space.
If you have a larger home with multiple bathrooms that might be in use simultaneously, a system boiler is often better as the hot water cylinder can handle higher demands without a drop in pressure.