Plumbing 101: Types of Central Heating Systems Simply Explained

By Lee Devlin, Director, Homecure Plumbers
Last updated 13 October 2026

Confused about what type of central heating system operates within your home? Thinking about upgrading? Find out how your home plumbing works and why it matters.

A quick Google search for the term ‘types of central heating systems’ is going to bring up some very varied and confusing results. You’ll find information on countless different types of heating concepts, boiler types and plumbing methods, all with perplexing jargon. It can’t really be that complicated, can it?

It’s not.

Our plumbers in London and central heating engineers are here to help simplify things and inform you of the basics behind the different types of central heating systems. No fuss, no confusion, no scary plumbing-specific lexicon. Just information anyone can understand, whether you are simply curious about plumbing basics, need to know what system is in your home or are considering options for upgrading.

We will start with the basics. How many types of boiler are there? Three main types, and you’ll find them in modern British homes. They are:

• Conventional (regular) boiler – a boiler with a hot water cylinder and a cold water tank in the loft. Sometimes called a gravity-fed or open-vented system.
• Combi boiler – heats the water for your radiators, and heats mains water on demand when you turn on a hot tap.
• System boiler – works with a sealed heating system and a hot water cylinder, with no tanks in the loft.

Looking for more information? We break down each type of central heating system in turn.

Conventional Central Heating

The conventional system used to be the most common type of central heating system in the home. Modern alternatives have resulted in a reduction of usage, especially in new builds, but you’ll still find conventional systems across many older houses and buildings.

So how does a conventional system work?

A cold water storage tank, usually in the loft, feeds a hot water cylinder, which is often in an airing cupboard. The boiler heats water that is pumped around the radiators and through a coil in the cylinder, which heats the stored hot water for your taps.

The hot water reaches your taps using the pressure created by the height of the tank in the loft, which is why it is often called a gravity-fed system. The heating itself is not simply flowing down from the loft: the boiler and pump circulate it.

This type of central heating system has seen a major decline in use for two reasons:

1. Gravity fed systems have limits of pressure, as they are subject to laws of physics. In order to increase pressure, additional systems must be installed

2. Heating of a hot water tank can be wasteful, as all the water may not be used yet energy is required to heat it and keep it warm.

Combi Boiler Systems

If conventional/gravity fed systems were the benchmark in previous decades, the combi boiler is the current title holder. This type of central heating system has risen to prominence in recent years thanks to its efficiency and compact nature.

So how do they work?

A combi boiler heats the water that circulates through your radiators, and heats mains water on demand when you turn on a hot tap. There is no hot water storage, so no cylinder or tanks.

This has a number of advantages over conventional types of central heating systems:

• As mentioned, combi boilers are efficient. You only heat the water you need. There is no wastage involved
• Hot water is fed from the mains, so on a good mains supply you get decent pressure at the taps without a pump. It depends on your incoming supply, though, and running several outlets at once reduces the flow at each
• Heating directly through the boiler means that there is no need for a hot water tank. This is especially useful in smaller properties, where housing a hot water tank would be difficult

Of course, there are disadvantages to combi boilers. They are more technologically advanced, with more complex inner workings, creating more potential to go wrong than the old workhouses that are conventional systems. Water pressure is also dictated by usage. Combi boilers are limited in their ability to produce hot water, which means you’ll experience poor flow rate if attempting to have two hot water taps run at once. This means it’s not suitable for large properties with multiple occupants.

Combi vs conventional boiler: side by side

The two most common choices compared:

Not sure which suits your home? Our boiler installation team can visit and advise.

System Boiler

How does a system boiler work?

A system boiler works with a sealed (pressurised) heating system. Instead of heating water on demand like a combi, it heats water stored in a hot water cylinder. This is usually an unvented cylinder fed straight from the mains, so there are no tanks in the loft.

Because the stored water is fed at mains pressure, several taps can usually run at once, which suits larger properties. The flow you get still depends on your incoming mains supply, and using several outlets together can reduce the flow at each.

Before we give this system too much praise, though, you must know there are two distinct disadvantages to operating this type of central heating system in your home:

1. Unvented cylinders cost more to install and maintain. They should be serviced in line with the manufacturer’s instructions by a suitably qualified engineer, and their design means installation is more involved, so it needs suitably qualified installers. They are a long-term cost.

2. If your local mains pressure is weak, this system will be a poor choice. Reliant on external factors beyond your control, installation of pressurised systems in a low-pressure area is not a good idea.

Which suits your home?

Combi boiler

Heating and hot water straight from one boiler. No tanks or cylinder.

System boiler

A boiler plus a hot water cylinder. No tanks in the loft.

Conventional boiler

A boiler, a hot water cylinder and cold water tanks in the loft.

All prices are + VAT and are “from” prices for parts and labour, fitted. They vary depending on the boiler make and model and job complexity, and we confirm a fixed price before work starts. Prices apply during office hours; parking or the congestion charge may be added.

Every installation comes with our own guarantee of at least 12 months (3 months on repairs), plus the manufacturer’s warranty: Vaillant 5 to 10 years, Ideal 5 to 10 years, Worcester Bosch up to 12 years and Baxi 5 to 10 years, depending on model.

Looking for boiler installation in London, or more information about the types of central heating system and what is right for your property? Get in touch with the experts at Homecure Plumbers today!