How does a combi boiler work?

What is a combi boiler?

A combi boiler (short for combination boiler), is a type of central heating system in a single compact unit.
Unlike traditional systems that include a separate hot water cylinder and boiler, a combi boiler heats water directly from the mains when needed, eliminating the need for a storage tank.

Combi boilers provide a “combination” of instantaneous hot water and effective central heating. These systems have two independent heat exchangers; one that links to your radiators (normally heated directly by the fuel source), and another that connects to your hot water supply (normally a water-to-water heat exchanger).

How do combi boilers work?

Combi boilers provide a “combination” of instantaneous hot water and effective central heating. These systems have two independent heat exchangers; one that links to your radiators (normally heated directly by the fuel source), and another that connects to your hot water supply (normally a water to water heat exchanger).

Combi boilers work by signalling a sensor once you’ve requested hot water which tells the boiler to burn fuel (whether gas, electric or oil). The heat exchanger then gets hot enough to heat the water when it flows over it.

The control valves within combi boilers work in different directions to one another. Therefore, the system will either transport hot water to your radiators or to your hot water tap – however, this will not be done at the same time and the hot water circuit usually takes priority. You can use heating controls to set your heating to your desired temperatures.

Unlike heat-only and system boilers, combi boilers do not require any additional tanks or cylinders to store hot water.

How are combi boilers fuelled?

Gas is commonly used in the UK to fuel combi boilers, as most domestic properties are connected to mains gas through an underground network.

Nevertheless, combi systems can be fuelled by oil or LPG, they can also be electric. LPG is typically supplied in bottles that need to be regularly replaced. Oil, in a similar manner, is usually stored in a tank which needs to be refilled on occasion.

What are the pros and cons of combi boilers?

The suitability of combi boilers varies based on individual preferences and household needs. While combi boilers offer significant benefits, they may not be the ideal choice for everyone.

Factors such as the size of the property, the number of occupants, and specific heating requirements play a crucial role in determining whether a combi boiler is the right fit.

Benefits of a combi boiler

Combi boilers come with a range of benefits that make them an attractive choice for many homeowners. These include:

• Space saving: No additional tanks or cylinders are required
• On-demand hot water: No need to wait for water to be heated up
• Compact: These systems can usually be fitted into a standard-sized kitchen cupboard
• Economical to run: Their high level of energy efficiency could help you save up to £200 on your annual energy bill ^[2]
• They are highly efficient: most combi systems have an efficiency rating of over 90%
• Quick and easy installations: no tanks or cylinders to install
• Safe & clean water: Water is delivered straight from the mains, so it can be viewed as fresher and safer than water that is stored.

Disadvantages of a combi boiler

It’s also important to consider potential drawbacks to help you make an informed decision. Some of these include:

• Water pressure: There can be a decline in water pressure if more than one outlet needs hot water at the same time
• No backup immersion heaters: Combi boiler systems don’t have backup immersion heaters to heat hot water in the event of a breakdown.

Warming to the idea of getting a combi boiler?

We’re working together with BOXT, who can help you decide on the best heating system for your home. With a range of gas boilers available from leading brands, a qualified BOXT engineer could provide you with a first-class boiler installation as soon as the very next day if you order before 4pm!

Get a fixed price quote today to find out how much a new boiler installation could cost—you’ll also receive a recommendation for the best boiler for your home.