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Central Heating Boilers: The Ultimate Buyers Guide

Are you looking for a new boiler to provide a reliable supply of hot water to your central heating system and water outlets?

Silly question, of course you are, who isn't?

There are three main types of central heating boilers available: combi boilers, system boilers and regular boilers

Central Heating BoilerThe exact type of boiler you require depends on a variety of different factors including the size and type of property you have, your hot water demands, age of your system, as well as the pressure of your mains water supply. 

So what type of central heating boiler is right for your home? In this guide we’ll explore the pros and cons of each and help you make an informed decision. 

Types of Central Heating Boilers 

Let's dive in...

Combination Boilers (Combi)

Central Heating Combi Boilers

By far the most common type of central heating boiler installed in the UK is the combination boiler (or, combi boiler for short). 

Combi boilers provide both hot water and central heating water from a single unit. This is typically wall hung. 

They're the heating dream ðŸ’Ī

How do combi boilers work? 

Cold water is taken directly from the mains water supply and heated by the heat exchanger within the boiler unit.

Central Heating Boiler Heat Exchanger

A combi boilers heat is produced through the combustion or burning of fossil fuels i.e. natural gas and oil. 

They do not require a separate hot water storage tank or a cold water tank in the attic. Instead, the hot water is provided from the unit itself, meaning that they are a great way to save space.

Learn all about combi boilers in our what is a combi boiler guide. 


Got a central heating boiler in a tight spot? Go for the Worcester Bosch CDi Compact.

Advantages of Combi Boilers 

Advantages of Central Heating Combi Boilers

  • The compact design makes them ideal for properties with limited space
  • Do not need a hot water storage cylinder
  • Do not need a cold-water tank
  • Hot water on demand
  • High efficiency
  • Straightforward installation
  • Can rely on mains water pressure

Disadvantages of Combi Boilers 

  • Typically, not suitable for larger properties with multiple bathrooms/or a high hot water demand
  • May not be suitable for areas that suffer from low mains water pressure

Heat Only (Regular) Boilers 

Central Heating Regular Boilers

Heat only or regular boilers are one of the oldest types of boilers and are composed of three main parts - the boiler unit, a hot water storage tank and a cold water storage tank. 

They provide both hot water to the central heating system and the storage cylinder, so are able to provide both hot water and heating water. 

How do regular boilers work?

The cold water storage tank is filled with cold water from the mains which is then fed into the hot water storage cylinder.

Regular Central Heating System

From there, it is then heated and stored ready to be used by the central heating system or delivered to hot water outlets. 

Advantages of Regular Boilers 

Advantage of Regular Central Heating Boilers

  • Good choice for properties with multiple bathrooms and high hot water demands
  • Ideal for areas that suffer from low water pressure
  • Good choice for those with older/traditional heating systems that cannot tolerate high pressure
  • Compatible with solar panels
  • Can be fitted with an immersion heater

Disadvantages of Regular Boilers

Disadvantage of Regular Central Heating Boilers

  • Since they require a cistern tank, they demand more space and limit boiler installation options. 
  • A cistern in the attic is prone to freezing during winter and if it leaks can be problematic.
  • Water pressure can be low since it relies on gravity. 
  • Installation is more complex. 
  • Hot water is limited since it can only use as much as the storage tank can store. 

System Boilers 

Central Heating System Boilers

System boilers are essentially an updated version of the regular boiler and are somewhere between the combi and the regular boiler. 

The majority of components are internalised, making installation options more flexible, for example, all parts such as the pump and expansion vessel are internal too, which also means it does not require a cold-water cistern tank and water is supplied to the boiler via the mains.


System boilers still require a hot water storage cylinder. They can provide both hot water on demand and heating water for your radiators.

Advantages of System Boilers 

Advantages Of Central Heating System Boilers

  • Recommended for properties with multiple bathrooms/hot water outlets - since water pressure loss is limited. 
  • Does not require a cistern tank in the loft. 
  • Internal components make installation easier.  
  • Compatible with solar thermal.  
  • Uses mains water pressure. 

Disadvantages of System Boilers 

Disadvantages Of Central Heating System Boilers

  • May not be suitable for areas that suffer from low water pressure. 
  • May not be suitable for older central heating systems that cannot tolerate high water pressures. 
  • If you are swapping from a combi, you need to consider where you will store the hot water tank.
  • Requires a hot water storage tank, so is not ideal for those with limited space. 
  • Once all hot water within the tank has been used, you have to wait for more water to be heated. 


Condensing vs. Non-Condensing Boilers 

Condensing or Non Condensing Central Heating

When on the hunt for a new central heating boiler, you may come across the term condensing boiler and non-condensing boiler.

No matter what type of boiler you are thinking of having installed, the law says that it must be a condensing one and so today there is no use in worrying about these terms, since all modern boilers are condensing. 

Condensing isn't a 'type of boiler' as such, it's more of a technical attribute

All condensing central heating boilers are at least 90% energy efficient, can harness excess energy to heat your home, are better for the environment and will help to reduce your heating bills.

For context, when you spend £1 on fuel only 10p is wasted, compared to older non-condensing boilers, which were around 70% efficient, this can make a substantial impact on your energy bills. 

Types of Central Heating Fuels 

Central Heating Fuel Types

Whatever type of central heating boiler you are looking at, they will require some form of fuel to generate heat energy. The type of fuel you use will depend on a variety of factors including whether your home is on-grid or off-grid. 

Gas Central Heating Boiler 

The majority of UK homes are connected to a gas supply via the national network, making a gas boiler an ideal choice for convenience and reliability. 

Advantages of Gas ðŸ‘

Per kilowatt hour (kWh) for gas is significantly cheaper than electricity, making it much more financially viable for most households. Although gas boilers are not 100% efficient and electric heating is, it is still cheaper to heat your home with gas. 

Disadvantages of Gas ðŸ‘Ž

Gas boilers are not 100% efficient and produce carbon emissions. 

Oil Central Heating Boilers 

Oil fuel is one of the most popular fuels for off-grid homes. It needs to be stored near your property in a storage tank and has to be refilled regularly. 

Advantages of Oil ðŸ‘

For those not connected to the network, oil fuel is one of the most reliable and financially viable alternative fuels that have a high heat output. 

Disadvantages of Oil ðŸ‘Ž

Oil fuel is not available on demand like those fuels available on the grid e.g. gas and electricity.

It also needs to be ordered and stored in a large tank kept close to your property. This also means you have to keep an eye on how much fuel you have remaining. 

Upfront costs for the storage tank can be substantial and since oil is highly flammable, it’s considered a hazard.

Electric Central Heating Boiler 

With electric boilers you have the option of powering them via the network or off-grid by using solar panels. 

Advantages of Electric ðŸ‘

Electric boilers are a good option for small properties with limited space and heating requirements since they are compact. They are also a great option for homes not connected to the gas network. 

An electric boiler itself is much more efficient than gas boilers, meaning the fuel used is converted to heat and not wasted to the environment. Yet, this does not mean they are more environmentally friendly. 

Electric boilers are much easier to install than gas, since they do not require installation of a flue and do not require a Gas Safe Engineer. Moreover, they do not rely on the combustion of fuel, so do not produce dangerous gases, such as carbon monoxide, so there is no risk of a hazardous leak. 

Disadvantages of Electric ðŸ‘Ž

Although highly efficient appliances, electric boilers are not inexpensive to run due to the high cost of electricity. For context, as of 2020, gas is currently half the price of electricity per kilowatt hour. 

Electric boilers are not efficient for heating up water and so if your property has considerable water demands e.g. if your property is large and has multiple water outlets it may not be appropriate. 

LPG Central Heating Boiler 

LPG or liquefied petroleum gas boilers use a mixture of hydrocarbon gases produced during the oil extraction and refining process. It is stored and transported in gas canisters. 

Advantages of LPG ðŸ‘

LPG boilers are very cheap to purchase, especially in comparison to oil boilers and gas boilers, being more than half the cost on average. 

Although LPG is a fossil fuel and is not carbon free, it is significantly less polluting than oil, producing up to 20% less carbon. In comparison to oil boilers they are significantly smaller, making them ideal for homes with limited space. 

Disadvantages of LPG ðŸ‘Ž

LPG is significantly more costly per kilowatt hour than both oil and gas. Since it’s not connected to a supply line, the fuel level has to be constantly monitored and a new tank reordered before all the fuel runs out. 

LPG gas needs to be stored in a tank, which can be purchased or rented from suppliers and must be stored in an appropriate location.  

Central Heating Boiler Costs 

Central Heating Boiler Costs

The cost of a new central heating boiler is dependent on a variety of different factors, these include the following: 

  • The type of boiler you have installed e.g. combi, regular or system
  • The boiler model you choose e.g. mid or premium range
  • If want to relocate your boiler e.g. from the garage to the attic
  • If you want to convert your boiler e.g. from combi to regular
  • Any add-ons you purchase e.g. filters, smart controls etc

One of the most common and straightforward type of central heating boiler installations is a straightforward combi swap i.e. replacing your old combi with a new combi. This is much simpler than replacing a combi with a system boiler. 


This is due to conversions being more complex to install, taking more time, requiring more labour and more materials. More everything.

The boiler model you choose also has an impact on the cost and at Heatable we offer more value orientated brands such as Alpha, as well as award winning, premium brands such as Worcester Bosch and Viessmann. 

Central Heating Boiler Size Guide

Central Heating Boiler Size Guide  

The boiler size refers to the boiler’s power and not its dimensions, which is measured in kilowatts (kW).

Typically, your boiler installer will determine the size you need based on the number of bathrooms and number of radiators you have in your property. 

Here are some examples of recommended boiler kW outputs based on your home’s estimated demands (Combi boilers only):

  Minimum kW Size  
What size boiler for... 1 Bath/Shower  2 Baths/Showers  
2 Bedroom House 26kW 29kW
3 Bedroom House 29kW 35kW
4 Bedroom House 29kW 35kW
5 Bedroom House 35kW 35kW

Curious to know which boiler brand performed worst? Find out in our report of the worst boilers

Central Heating Boiler Prices 

Central Heating Boiler Prices

Some people are interested to know the stand-alone central heating boiler costs.

A new combi boiler or system boiler can cost between £600-£900 for a budget model, £900-1,200 for a mid-range model and £1,000 - £2,000 for a premium model.

A regular or heat-only boiler can cost anywhere between £500 - £2,000 depending on size and quality. 

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Heatable is registered in England and Wales No. 08804726 (VAT No. GB205805920 ). Trading address is 1 Station Road, Great Sankey, Warrington, Cheshire, WA5 1RH. Heatable acts as a credit broker (not as a lender) and offers credit products through a panel of lenders. Heatable is authorised and regulated by the Financial Conduct Authority (reference no. 805259).

[1] Price based on a like for like combi swap in a 2 bed, 1 bathroom terraced home with a standard flue

[*] Installation dates are subject to installer availability

[āļĒāļ™] only available on combi boiler installations

Financial Support: If you are in receipt of certain benefits, you may be entitled to claim a free boiler grant.