Unlike traditional boilers that use a water storage tank, a combi-boiler draws all of its water directly from the mains supply.
Combi-boilers provide hot water on demand plus, since combi-boilers eliminate the need for a water storage tank, you also gain additional storage space in your home.
One of the most popular things about combi-boilers is the fact that you can heat water ‘on demand’, you do not have to heat an entire cylinder of water for small tasks that require minimal usage.
Also since water is not stored in a tank for long periods of time, combi-boilers also reduce the risk of Legionnaires disease from bacteria growth. However, since combi-boilers lack a water storage tank, large homes with many occupants will suffer. This is because water from the mains will not provide enough water to feed multiple water outlets., thus, when two or more people turn on a tap or shower simultaneously, the water will dramatically drop.
This isn’t so much a problem with a traditional boiler since the backup water tank is sufficient to meet this level of demand. If more than four people live in your home, we recommend you stick with a traditional boiler for this exact reason.