Combination boilers are completely different than the more traditional form of system set up known as conventional systems, where it takes its water from a tank that is usually in the loft of your home. This process is done by a ball valve without requiring regular maintenance as when the system requires additional water the ball valve that is fixed inside the storage tank drops and allows mains water in. This is different with a combination boiler because it is a sealed and pressurised system so you will have a manual filling device (i.e – filling loop). This allows mains water to be injected into your system and re-pressurised to the desire ‘bar’ of pressure before closing the device and once again sealing the system.

Every pressurised system, whether Combi or System will incorporate a pressure gauge. This needs to be checked monthly and re-pressurised if necessary. 

Your boiler manufacturer’s instructions will advise you on the correct system pressure to have but most systems are between 1 and 2 bar.

There are huge advantages to having a pressurised system. Mainly, as the system is sealed then the water within it can’t become contaminated. Contaminated water can cause a number of issues such as blocking your heat exchanger within your boiler or restricting the efficiency of your radiators.

System Pressurising