Boiler Buying Guide

Save up to £310 every year by upgrading to a new A-rated boiler*

Our boiler buying guide can help you find the right replacement boiler or a new boiler to suit your home and central heating system requirements. We'll show you a list of boilers to choose from that will generate enough heat to keep your home at a comfortable temperature and provide enough hot water for the entire household.

Once you have your list of suitable boilers, simply add the one that suits you best to your basket and checkout when you are ready.

What type of boiler do you have?

There are three kinds of boiler: combi boilers, regular boilers and system boilers. Learn about all three of these below.

Combi Boilers

  • Instant/unlimited heat and hot water.
  • Suitable for small to medium-sized homes.
  • Installation costs are cheaper than system and regular boilers. Cylinders and tanks are not required.
  • Not suitable for homes with low incoming water pressure (1.0 bar min).

A Combi Boiler, or Combination Boiler, is generally considered to be the UK’s most popular type of boiler. A Combi Boiler is a compact and highly efficient unit, which can supply a busy domestic household with all the heating and hot water supplies it will ever need, whilst guaranteeing significant savings on running and installation costs. Hence why many of us prefer to choose the Combi Boiler over all other types of boiler.

Unlike a conventional heating and hot water system, a Combi system does not store domestic hot water. It heats water directly from the cold mains, as you use it. There is no requirement for a hot water cylinder, a tank in the loft, or the connecting pipe work so there is less risk of freezing and flooding. This will not only save space but also reduce hot water costs, which can account for up to 60% of a typical domestic fuel bill. A Combi Boiler also supplies hot water at mains pressure, giving you exhilarating power showering, without the need for a pump.

Combi Boilers are not suitable for larger properties with 3, 4 or more bathrooms.

Combi Boiler

Regular Boilers

  • Suitable for homes with multiple bathrooms.
  • Suitable for large homes.
  • Installation costs are higher than system and combi boilers.
  • Space required for the cold water tank, hot water cylinder and other heating components.

Regular Boilers, otherwise known as Heat Only Boilers, Conventional Boilers, or Open Vented Boilers are used in a more traditional central heating system. If you are looking to replace an old boiler, then this may be the system that you currently have.

A Regular Boiler works on the basis of ‘heating only’ and requires a separate hot water cylinder, typically located in an airing cupboard. Additionally there are two feeder tanks, typically located in the loft area. One of the tanks is for domestic hot water that feeds to the hot water storage cylinder, and the second tank is required for central heating.

Having a regular boiler system means that, unlike a Combi Boiler system, the hot water flow rates tend to be higher as the hot water is already stored in the hot water cylinder. This allows the use of several hot water outlets being operated at the same time within the property. Due to the number of components that a Regular Boiler system requires it will use up more space than any other heating system.

Regular Boiler

System Boilers

  • Suitable for homes with multiple bathrooms.
  • Suitable for large homes.
  • Integrated sealed system, no tank in the loft.
  • Installation costs are higher than combi boilers.
  • Space required for hot water cylinder.

Sealed System Boilers work in a similar manner as Conventional Boilers, where they indirectly heat a separate store of domestic hot water. System boilers are most commonly used for use with Unvented Cylinders. Unvented Cylinders don’t require a separate header tank in the loft, instead, they are filled directly from the mains water supply and are completely sealed.

Although similar in many ways, the difference between a Sealed System Boiler and a Conventional Boiler (Regular Boiler) is that the System Boiler incorporates all of the major components built-in, including an expansion vessel and modulating pump. Generally, all components are pre-wired, pre-plumbed and pre-tested for greater reliability, as well as a quicker and neater installation.

System Boilers

How many bedrooms and radiators are there in your home?

The size of your home and the number of radiators will impact which boiler you choose.

  • Small boilers – best for flats
  • Medium-size boilers – good for homes with three or four bedrooms or roughly ten radiators
  • Large boilers – best for homes with five or more bedrooms

How many bathrooms are there in your home?

Please count all bathrooms, including ensuite bathrooms but excluding cloakroom bathrooms. The more bathrooms you have and the more frequently they are used, the more powerful your boiler will need to be.

What type of flue do you need for your boiler?

You will need a new flue for your new boiler. The flue type is determined by where your boiler is installed. Boilers installed in the kitchen will typically have a flue that terminates on an external wall, requiring a horizontal flue. Boilers installed in an airing cupboard upstairs will typically have a flue that terminates on the roof, requiring a vertical flue. See the diagrams below to match your flue type. We recommend that a Gas Safe registered engineer performs a site visit to determine all necessary components.

Boiler Flues

The flue system is an essential component of your boiler set-up. It provides your appliance with adequate oxygen in order for it to operate safely and efficiently, as well as providing an exhaust for the products of combustion to disperse safely away from your property.

Depending on the location of your boiler you will need to consider what type of flue system would be required with space restraints and gas safe regulations in mind.

If your boiler is located on an external wall then you would normally be fine with a standard horizontal flue that comes with a tight flue bend that is fitted directly to the top of the boiler. If space is an issue then you may opt to go for a direct rear flue. In this scenario, the flue would be installed directly behind the boiler and wouldn't have a tight bend on the top.

If the boiler is located on an internal wall or centralised in the property then a vertical flue system would normally be used. This system would normally take a vertical route through the loft space and terminate on either a flat or a pitched roof.

If your boiler is situated in such a way that you couldn't terminate the flue through the roof space and the route is met with installation constraints then you may need to take it vertically first but then run it on a horizontal plane whereas it would terminate through an external wall. This setup would require additional flue components.

Always remember to consult a Gas Safe engineer to ensure the correct flue system is used for your boiler.

What is most important to you; the boiler warranty, the lowest price available, or the best of both?

The cost of your boiler will vary depending on its lifespan/warranty. Some boilers include a warranty of up to 10 years. Choose the longest warranty available for peace of mind.

Gas Safe Register

It is a legal requirement that all boiler installations are carried out by a Gas Safe registered engineer.

Safe Register is the official list of gas engineers who are qualified to work safely and legally on gas appliances. Always check your engineer is on the Gas Safe Register.

Gas Safe Register

Please note - All boilers available from are A-Rated high-efficiency condensing boilers.

*Source Energy Saving Trust. For more information please refer to our Saving Money on Heating Bills Infographic.