Types of Boilers: Which Suits Your Home?

When central heating became commonplace in the UK in the 1970s, most homes got the same thing:

• A conventional boiler
• A hot water cylinder
• A tank in the loft. 

Since then, the technology has split into three distinct types: Combi, system, and conventional.

Each is designed for a different kind of home. 

Choosing the wrong one will reduce your comfort and increase your energy bills.

Combination (combi) boilers

Combi boilers are the most popular type of boiler in the UK.They are a single unit that manages both your heating and hot water.

Unlike other boiler types, they don’t come with a separate water cylinder or storage tank. Instead, they heat water directly from the mains whenever you turn on a tap (or shower).

How combi boilers work

When you turn on a hot tap or activate your heating, a combi boiler ignites its burner. Cold water flows from the mains directly through the heat exchanger, heating it almost instantly.

(Average) installation costs

A new combi boiler typically costs £1,500–£3,000 installed, depending on the brand and any additional pipework required.

Advantages of combi boilers

Combi boilers are compact and usually fit inside a standard kitchen cupboard.

They are extremely convenient: By heating water on demand, they essentially provide an unlimited supply of hot water from a single tap or shower at a time.

Installation is simpler and cheaper because there are no external tanks or cylinders to plumb. 

Additionally, they are energy-efficient and carry high A-rated performance markings.

Disadvantages of combi boilers

Combi boilers struggle to supply multiple taps simultaneously. So, if someone turns on a tap whilst you are showering, your water pressure and temperature can drop.

They also rely on mains water pressure rather than gravity. So, if there’s a weak mains supply, there will be poor water power. 

In short, they are not the best choice for larger homes with multiple bathrooms.

System boilers

System boilers suit busy households with high hot water demands. 

Unlike a combi, a system boiler requires a separate hot water storage cylinder. This is typically housed in an airing cupboard. 

However, unlike convention boilers (see below), they don’t require a cold water tank in the loft.

How system boilers work

A system boiler heats water and pumps it directly to your radiators and hot water cylinder. 

The cylinder stores the water under pressure, so it’s ready for your taps. 

And most of the major heating components (pump, expansion vessel, etc.,) are built directly into the boiler casing.

(Average) installation costs

Expect to pay £1,800–£3,500 for an install, with additional costs if the hot water cylinder needs replacing.

Advantages of system boilers

System boilers supply multiple taps and showers simultaneously without a drop in pressure. This makes them suitable for homes with several bathrooms. 

Components are pre-plumbed inside the casing, so installation is relatively quick. 

They don’t require an attic tank, which removes the risk of pipework freezing in your loft during cold weather.

And are fully compatible with solar thermal systems.

Disadvantages of system boilers

System boilers’ hot water supply is limited by their cylinder size. So, when the tank gets emptied, you have to wait for the system to reheat. 

They also require dedicated and well-insulated cupboard space for the cylinder.

Conventional boilers

Conventional boilers (also known as regular or heat-only boilers) are common in older, larger UK properties. They require a hot water storage cylinder and two water tanks in the loft.

How conventional boilers work

Loft tanks feed cold water down to hot water cylinders. 

The conventional boiler then heats the water, which is stored in the cylinder and circulated around your radiators by an external pump. 

Meanwhile, attic expansion tank maintains the system’s water level safely.

(Average) installation costs

Installation typically runs £2,000–£4,000, reflecting the more complex pipework and the potential need to replace the cylinder and loft tanks.

Advantages of conventional boilers

Conventional systems manage high hot water demands across multiple bathrooms simultaneously.

They are a practical replacement if you are upgrading an older property with delicate pipework. (This pipework might not be able to withstand high modern mains pressure.)

They can also use a backup immersion heater. This ensures you still have hot water if the boiler breaks down.

Disadvantages of conventional boilers

Conventional boilers require a lot of space: Loft space for two tanks and cupboard space for the cylinder. 

They don’t provide instant hot water. You must programme the system in advance. Reheating takes time once empty. 

The setup is more complex to install than other boilers, due to the external pumps and pipework.

All new UK boilers are condensing by law

Homeowners researching boiler types often ask where condensing boilers fit into the mix. 

It is important to understand that condensing is not a distinct type of system. Rather, it is a technological standard.

By law, every new gas boiler installed in the UK must utilize condensing technology. Condensing boilers feature a secondary heat exchanger. 

This captures the latent heat from escaping water vapour and exhaust gases, recycling it back into your system instead of venting it outside. 

This makes modern boilers incredibly efficient, with seasonal ratings exceeding 90%.

Which boiler type is right for your home?

Selecting the perfect system depends on several factors. You can use this checklist to determine which boiler fits your household:

Property size and bathrooms

Combi boilers suit small homes with one bathroom. System boilers are ideal for medium properties with two bathrooms. Conventional systems suit large homes with three or more bathrooms.

Mains water pressure

Choose a combi or system boiler if your mains pressure is strong. 

A conventional boiler is a safer option if your mains pressure is weak or your pipework is old (1970s or before). This is because as it operates on gravity rather than mains pressure. Fitting a combi or system boiler may require pipework upgrades.

Available space

A combi boiler is your only practical option if you have no loft space or airing cupboard. A system boiler needs cupboard space for a cylinder, whereas a conventional boiler needs both cupboard and loft space.

Existing pipework

A conventional boiler is suitable if your home has older pipework.

Alternative heating systems

Alternatives to traditional boilers are growing in popularity.

Heat pumps extract warmth from the outdoor air or ground. They come in two main forms: ground source (which require outside space to install) and air source (which can fit on walls).

Hydrogen-ready boilers are designed to run on a blend of natural gas and clean hydrogen in the future. And thermal solar panels use sunlight to heat water directly.

What type of boiler do you already have?

If you have just moved into a new property, you can easily identify your heating system by checking for these physical clues:

• The cylinder test: Look in your cupboards. If you do not have a hot water cylinder, you have a combi boiler. If you have a cylinder but no cold water tanks in your loft, you have a system boiler.
• The loft test: If you have a hot water cylinder and physical water tanks in your attic, you have a conventional boiler.

You can also find the exact model name and number printed on your boiler’s casing or data plate. Looking this up online will instantly confirm your system type.

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