Boiler Types Explained

There are 3 main types of boiler in the UK: Combi, System and
Regular (or Heat-only). We've explained each below.


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Boiler Types Explained

Witten by Bernard Morgan (Engineer) & Adam Apperley (Marketing). Published: January 29, 2021. Updated: March 22, 2024

In the UK, there are three main types of boiler commonly installed into homes. These are combi boilers, system boilers and conventional (aka heat-only or regular) boilers.

  • Combi boilers do everything in one unit. They heat your home and produce on-demand hot water. This means no hot water tank.
  • System boilers are the same as combi boilers, but they don’t produce hot water on demand. You will require a hot water tank.
  • Conventional boilers are similar to system boilers but with an additional tank in the loft to add pressure as they don’t use mains water pressure. Back boilers are a type of conventional boiler.

Are you unsure about which boiler you have? Read our guide to quickly figure out what type of boiler you have.

Combi boilers explained

Combination Boiler

Combi (combination) boilers are generally considered to be the easiest and most cost-effective boilers. Combi boilers have no tanks or cylinders.

They heat water for central heating and hot water as required. The central heating portion of a combi is on a pressurised closed loop. For hot water, the mains supply is fed directly to the boiler. This means no hot tank to refill and a constant hot water supply at mains pressure.

Want more detail? Looking at the diagram:

  • The combi boiler has 4 water pipes.
  • The heating system feeds the radiators with hot water and cooler water comes back to be re-circulated.
  • You can pressurise the heating system with the filling loop (these can be internal or external to the boiler).
  • Cold water mains feeds the cold taps and the boiler. The boiler heats up the cold water for hot taps and showers.

The negatives with this type of boiler:

  • If your incoming cold-water pressure is too low, it may not work correctly.
  • Hot water pressure will fall with each tap or shower is use. It may also stop heating water if the pressure falls too low to stop the boiler overheating.
  • Larger homes with high hot water demands may not be able to be supplied by a combi boiler.
  • If they stop working, there is no backup hot water option.

Combi boilers are suitable for most households, but not all. They are often a great choice as fewer things can go wrong on central heating systems and are cheaper to run.

If you have high hot water demands a storage combi boiler may be a great option for you Find out more here >

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System boilers explained

System Boiler

A system boiler heats your home and produces hot water like a combi boiler. But unlike a combi boiler the hot water it scheduled and is stored in a hot water tank – it is not created on demand.

The boiler has an integrated pump and expansion vessel to replace the cold tanks associated with conventional boiler systems. Other integral components include a system programmer and valves.

System boilers are easier to install than conventional heating systems.

Want more detail? Looking at the diagram:

  • The boiler heats the water in the heating loop which circulates around the radiators and then heads back to the boiler to be reheated.
  • When the boiler is set to produce hot water, a valve in the pipework redirects the hot water to the hot water tank. This than transfers the heat to the water in the tank.
  • There is no cold water feed into the boiler.
  • Hot water is fed from the hot water cylinder under the same pressure as your mains water pressure. However, additional pumps could be added.

The main negatives of this type of boiler:

  • The boiler is costly to install as a new cylinder is required.
  • More components to go wrong.
  • More pipework and space required.

Conventional boilers explained

Conventional Boiler

Conventional boilers are being slowly replaced by combi and system boilers where appropriate. But, if your cold water pressure is low, staying with this boiler may be the best option. Conventional boilers are also known as ‘Regular’ and ‘Heat-only’ boilers.

The system is being fed by header tanks in the loft. A pump is used outside the boiler to pump water around the radiators, ensuring the central heating system is working. The hot water is stored in a cylinder which supplies hot water when required.

In addition to this, these systems require hard-wired control systems.

Want more detail? Looking at the diagram:

  • The boiler heats water and pumps it around the radiators using the pump. There is no pressure gauge on the boiler.
  • The cold water header tank creates pressure in the heating loop and hot water feed.
  • Hot water is created by diverting the heating water through a heating coil in a hot water tank.

The negatives with this type of boiler are:

  • More expensive to operate.
  • More components to go wrong.
  • Can suffer from low water pressure on taps close to the tank.

If you need a new boiler, whether it’s a combi, system or regular boiler, get an online quote (it takes less than 1 minute), and you’ll get an instant price. But why choose Boilerhut:

  • Quick central heating system installation. Next day boiler installation.
  • Combi, System & Regular boilers installed, back boilers decommissioned and replaced.
  • ‘Excellent’ 5* customer satisfaction on Trustpilot.
  • Finance options available for central heating or boiler installation.
  • 10 to 12-year warranty on boilers.
  • Fixed prices. No hidden extras.
  • Get up to three boiler quotes for different-tier boilers.
  • Instant, no-obligation quote in less than 1 minute.

Type of boilers that Boilerhut install

We will supply and install everything that is required for a full central heating system.

Combi Boilers

Combination boilers – more commonly known as combi boilers, are the most popular boilers sold in the UK for central heating and domestic hot water. Storage combi boilers also fall into this category.

System Boilers

System boilers work on a closed heating system, and only require a boiler and an unvented hot water cylinder for storing hot water.

Heat only / Conventional boiler - Types of boiler | Boilerhut
Conventional Boilers

A conventional boiler is a type of boiler that requires a boiler unit plus a hot water cylinder and a cold water storage tank.

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