What is a Combi Boiler and How Does It Work?

Combi boilers, also known as combination boilers in the United Kingdom, are the most widely used type of boiler.


Combi boilers are usually mounted as a single appliance and can supply all heating needs. However, they are also very efficient in providing hot water for sanitary purposes such as washing up, bathing, showering, cooking, and hand washing.


These devices not only provide significant savings on installation but also offer lower running expenses, making them the ideal choice for larger residential properties and commercial buildings that require hot water or heating.


This combi is more efficient than traditional systems and heats water immediately when turned on by the hot tap.


How a Combi Boiler operates.

A combi boiler incorporates a central heating and water heater. Water is heated by an integral heat exchanger from the cold mains. If the room thermostat signals the boiler to start, it will fire up when the temperature drops below a set point. The central heating system can then heat the water by injecting heat into the boiler. The boiler can also’modulate,’ or turn itself off, when you reach the thermostat setting point. This maintains the temperature at the desired temperature, which is a cost-saving measure.


A valve located in the combi boiler directs heat from the hot tap to the hot supply. The valve produces hot water until the tap shuts off. Although heat can be delivered to the hot water taps and central heating system simultaneously, it cannot be both.



A condensing or gas-condensing stove is required to replace a boiler, or to install a new one.


A non-condensing Boiler only has one heat Exchanger. Therefore, the temperature of the flue from a boiler that is not condensing could rise to 250 degC. This is heat that could not be used and could be recycled to improve the system’s efficiency. Condensing-gas boilers can use the heat from these waste gases to heat water.

A combi boiler installation is a closed-system boiler that operates differently to an open vent. Any air entering the stream can affect the heating, boiler and pump. If the boiler loses additional pressure, it will shut off and display an error message. Unexpected pressure loss could be caused by a loose, rusted or damaged connection.



A filling circuit is used to return the combi boiler’s water pressure to the desired levels. A boiler will usually have a pressure gauge located right next to its display. The combination boiler pressure should never drop below 1 bar nor rise above 3 bar. The safest range between 11/2 and2 bar is



How do you fuel your Combi Boiler?


Most UK Commercial properties are connected via underground networks to mains-gas, so gas can often be used to fuel a combi boiler. However, this is not all that is possible. LPG or oil can also be used to power a combi system. LPG is normally delivered to you in bottles that have to be refilled on a regular schedule. You store oil in the same way.


Combi Boilers are on the verge of extinction


The UK government seeks to change how we heat our homes in order to reduce greenhouse gas emissions. According to recent statistics, heating makes up around 40% of the UK’s total energy consumption. We can reduce our carbon emissions by using fuels such as hydrogen.



Hydrogen could be used as an alternative fuel to Natural Gas and LPG. LPG, oil, and natural gas all produce carbon dioxide from the combustion. There are many options for how hydrogen can be obtained as a fuel source. This includes an electrochemical process in which hydrogen is separated from its source fuel. In such a case, carbon emissions would need to been captured and permanently contained.
What Combi Boiler Should You Buy for Your Commercial Application?


A combi boiler will need enough mains to allow for a reasonable water flow rate. Too low mains pressure can cause hot water to only trickle out of the tap. If your mains is low or you have more than one washroom, system boilers may be a better choice.



You should also make sure that the boiler heats up to your specific needs.

Combi boilers produce heat for both central heating and domestic hot water. Producing hotwater requires more work and heat than heating radiators. Because of this, your boiler options will depend on the hot water output. A Gas Safe Registered Installer can help you choose the right boiler for your Commercial Heating & Hot Water needs.



What are the main benefits of a Combi Boiler


These are the advantages of combi boilers

They are easy-to-use – Most combi boilers include simple controls. The temperature and timing controls allow you program the heating system so that it turns on only when you are using it. You can choose the desired temperature for your space at any given moment. This will increase comfort and control, as well as reduce your fuel bill.


The boiler is all that is needed to heat the radiators or supply hot water to the taps.


A combi boiler does away with the need for a water tank and a hot-water storage cylinder. This allows it to be installed in a shorter time, saving you money and time.


Low maintenance costs: The warranty/guarantee of the boiler manufacturer covers both the integral heating system and hot water functions.


No waiting for hot water


What are the downsides to a Combi Boiler


They will not work in properties that have low flow rates or incoming pressure.


While hot water flow rates decrease when hot water goes to more than one outlet at the same time, this is usually not an issue in properties with multiple washrooms.


A combi boiler does not include backup immersion heaters that heat the hot water in case it breaks down.

Do You Need a Different Hot Water Cylinder?

No, you do not. No, the combi boiler does not heat the water.


Can you install a Combination boiler yourself?

Gas Safe Registered Installers must not install gas appliances.


What accessories or controls are required for combi boilers?

Building Regulations now require every boiler installation to have a timer as well as controls.



1. The seasonal heating efficiency of the space must be less than 92% (A rating on ERP label).

2. All installations need to be managed in terms of temperature and time.

3. In every combi boiler installation, one must be:

* Compensation for bad weather

* Compensation for Load

* Heat recovery using flue gas

* Automation and optimization through smart control