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What is central heating and how does it work?

A large majority of homes across the UK have some form of central heating system. You may not realise it, but it’s an essential part of your home as it provides you with heating and hot water whenever you need it.

What is a central heating system?

When your boiler receives a demand for central heating (via a thermostat), hot water is generated which then travels through the pipes around your home to your radiators or underfloor heating pipes helping to heat your home.

The radiators or the under floor pipes then heat up making the room feel warm and comfortable. A central heating system also provides hot water, this could be stored hot water, usually in the form of a cylinder or instant hot water if you have a combi boiler.


What type of boiler do I have?


Combination (combi) boilers provide both heating and hot water from the same unit, without the need for hot water storage. They are usually found in smaller properties as they don’t require space for a cylinder. "Combi boilers are a relatively modern type of heating appliance which can be quite energy efficient, and in turn cost-effective, depending on your usage.

This type of boiler heats your home and supplies hot water to your taps almost instantly. For heating, the water is heated up to the desired temperature which is then transferred to the radiators to heat up the room. Learn more about combi boilers here.



Conventional boilers, also known as heat only and regulat provide central heating and hot water which is kept in a hot water cylinder. This type of boiler is ideal for homes who have high hot water demands from multiple sources but also low water pressure.

A conventional boiler works by cold water traveling from the mains supply to the cold water cistern (usually found in the loft next to the feed and expansion tank). The water then passes into the feed and expansion tank to ensure there is always the right amount of water stored in the boiler.

Once the cold water moves down into the boiler, it passes over the heat exchanger where the heat is transferred to the water. The heated water is then pumped through the pipes to the radiators to heat the property. Learn more about conventional boilers here.


System boiler

Similarly to regular boilers, system boilers also require a separate cylinder to store hot water. The boiler itself is smaller in size and is ideal for larger homes with multiple bathrooms that require hot water at the same time.

They work by cold water entering the system boiler directly from the mains water supply, the water then passes over the heat exchanger inside the unit which transfers heat to it. Once the water has been heated to the temperature set on your thermostat and is then transferred into the radiators using a central heating pump. Learn more about system boilers here.


How does my boiler supply hot water:

Depending on your boiler, it will supply hot water in different ways.

With combi boilers, hot water is always available whenever a hot tap is switched on and so it doesn’t require a separate timer.

There is a sensor for detecting hot water and the heating demand is set through from the thermostat. The water is then heated up inside the boiler via the heat exchanger and travels from the boiler to the outlet through your hot water pipes to give you hot water on demand.

For a central heating system with a hot water cylinder, the regular or system boiler needs to know when to switch on and when to switch off again. This is similar to your heating, your hot water will be on a timer.

The boiler needs to know when the hot water in the cylinder is at the right temperature. To do this the cylinder will also have a thermostat which measures the temperature of the water inside it. When it hits the right temperature, the boiler will switch off. Without this thermostat the temperature inside the cylinder could get too hot and could pose serious danger of scalding.

Heat is transferred into the water in the cylinder through a long coiled tube (which looks like a big spring) which sits in the water. Hot water from the boiler is pumped through this long coil and the heat is transferred into the water making it hot and ready for use.


Benefits of a heating control

In most homes, central heating systems will be controlled via a thermostat. Glow-worm offers a wide variety of controls to suit your needs. These range from easy to use analogue timers to smart thermostats, which can even detect the outdoor temperature to ensure it is comfortable.

A thermostat allows us to control our heating and hot water to suit our lifestyle. You can programme your thermostat to come on at a time that suits you to ensure your home is at a comfortable temperature.

Upgrading to a smart heating control, like the MiGo, offers further flexibility as it is easier to control your home's temperature. Using an app, you can turn your heating on at a touch of a button even if you’re not at home. Learn more about Glow-worm controls here.

How can I look after my central heating system?

It’s important that you take the necessary tips to look after your central heating system to make sure it is working efficiently.

If you notice any cold spots on your radiators when your heating is turned on, there could be an air lock that is affecting your boiler's performance. Doing this every so often could also save energy as your boiler isn’t having to work as hard to heat your home.

Read our step by step guide on how to bleed a radiator.

You should have your boilers serviced every year by a qualified heating engineer. An annual service will ensure that your system is working efficiently and prevents any future problems from arising. The heating engineer will do a thorough check of the appliance and identify any concerns. Book a Glow-worm boiler service here.

If your boiler keeps breaking down or you notice it’s not performing to a maximum efficiency, it might be time for an upgrade.

We recommend opting for the same type of boiler that you already have so you don’t need to change the current system. This will keep the installation cost down and you already have the space. However, if your central heating system is old, you may want to upgrade it, however this can be more costly.

Need more advice?

If you want to learn more about our boiler range or need help choosing the right heating control for your heating system, please contact your local Glow-worm installer.