Combi boilers are the most popular type of boiler sold in the UK. Water is heated instantly when a hot tap is turned on, so there is no need for a hot water storage cylinder, making them the perfect choice for homes where space is at a premium.
A combination boiler combines a water heater and central heating boiler in one compact casing. If the room thermostat sends a signal to the boiler to fire up because the temperature has fallen below the set point, the boiler will fire up so that heat can be pumped into the central heating system. As the thermostat set point is reached, the boiler will ‘modulate’ or turn itself down, keeping the heating at the right temperature and saving energy.
When someone turns on a hot water tap, a valve inside the boiler diverts the heat into the domestic hot water supply, providing hot water until the tap is turned off, when the valve returns to the ‘central heating’ position. The heat can be directed to either the central heating system or the hot water taps but never at the same time.
Combi boilers require sufficient mains water pressure to deliver a good water flow rate; low mains water pressure means hot water will merely trickle. If your mains water pressure is low or you have more than one bathroom, a System boiler might be a better option for you.
It is also important to ensure that the heat output of the boiler is correct for your needs. Combi boilers have two heat outputs: one for Domestic Hot Water and the other for Central Heating. More effort and therefore more heat is required to produce hot water than to heat the radiators, so it is usually the hot water output that determines your choice of boiler.
A Gas Safe registered installer will be able to help you determine what boiler you require to meet your needs; you can locate your nearest installer by using our Find an Installer tool.
No, because a combi boiler only heats water when a tap is turned on, so there is no need to store the hot water. View our combi boiler range here.
Yes, we have some dedicated LPG models of combi boiler so that homes off the mains gas grid can enjoy all the benefits of our high-efficiency combi boilers. View our combi LPG range here.
When the Building Regulations changed in April 2018 (commonly known as Boiler Plus), timer and controls now need to be fitted as part of every boiler installation, along with extra energy efficiency measures for combi boilers.