General boiler info

What are the different types of boilers?

We explain about the different types of boiler and their pros and cons, so you can make an informed decision on which type of boiler you need when you come to replace yours.

What is a condensing boiler?

The term ‘condensing’ refers to the technology inside the boiler rather than the actual boiler type. Since the Building Regulations changed in 2005, all new installations have had to be condensing boilers rather than standard efficiency boilers, because they are at least 25% more efficient than the older models.

Condensing boilers have a bigger and more efficient heat exchanger that is able to recover almost all the heat out of the gas it burns, so that very little useful heat is lost through the flue. This means the boiler doesn’t need to work so hard or use as much fuel to heat your home or hot water, saving you money on your fuel bills and reducing carbon emissions. Because it doesn’t get so hot, the flue of a condensing boiler is usually made of plastic, rather than metal, like the flues of non-condensing boilers.

Because most of the heat is removed from the flue gas and reused, the left over liquid tends to ‘condense’, hence the name, and this liquid is drained away from the boiler into a waste pipe through a white plastic condensate pipe that usually comes out of the bottom of the boiler. 

How can I tell if I have a non-condensing boiler?
  • Your flue is made of metal rather than plastic.
  • There is no white plastic condensate pipe coming out of the bottom of the boiler.
  • You have a permanent pilot light – modern condensing boilers have electronic ignition that fires up the boiler when it turns on so there is no need for a pilot light constantly burning gas.

If your answer is yes to any of these, then you have a standard efficiency boiler and could save up to £305 a year by replacing it with a high efficiency model.

What is a combi boiler?

Combi, or combination, boilers are the most popular types of boiler in the UK. All the components needed for your central heating and hot water are combined in the boiler’s compact casing. The boiler switches from central heating to hot water when a hot tap is turned on, providing instant hot water whenever you need it.


  • You only heat the water you need.
  • No need for a hot water storage cylinder or tanks in the loft.
  • Perfect for homes with limited space.
  • Hot water is delivered at mains pressure.


  • Hot water will only be available at one tap at a time.
  • Not suitable for homes with more than bathroom used at the same time.

What is a system boiler? 

System boilers include the expansion vessel and pump inside the boiler casing. They need a hot water storage cylinder but do not need water tanks in the loft. They are suitable for homes with more than one bathroom and a high demand for hot water. 


  • No need for tanks in the loft, reducing the risk of frozen pipes and leaks.
  • Plenty of hot water from several taps at the same time.
  • Perfect for homes with more than one bathroom, or with a high demand for hot water.
  • Compatible with most solar thermal systems.


  • You need space for the hot water cylinder.
  • You need to wait for the water in the cylinder to heat up before you can use it.

What is a heat only boiler? 

Heat only boilers are also known as regular, traditional, conditional or open vent boilers. They need a feed and expansion tank and a cold water storage tank in the loft and a hot water storage cylinder and separate pump, usually housed in the airing cupboard.


  • A good option for areas where the mains water pressure is low.
  • Perfect to replace an old existing boiler while retaining the existing central heating system.
  • Good for homes with more than one bathroom, or with a high demand for hot water.
  • Plenty of hot water from several taps at once.
  • Compatible with most solar thermal systems.


  • You need space for the hot water cylinder.
  • You need to wait for the water in the cylinder to heat up before you can use it.
  • Tanks in the loft could be susceptible to freezing.

What other kinds of boiler are there?
  • Electric boilers – much more energy efficient than gas boilers, but electricity is more expensive to buy. They do not have a flue, so are more suitable for homes where a flue is not an option, such as tower blocks. Check out electric boilers from our sister company Heatrae Sadia.  
  • Oil boilers - an alternative to homes that do not have mains gas. An oil boiler will typically be more expensive to run than gas.
  • Solid fuel or biomass – biomass pellets or blocks are much more sustainable than other forms of fuel; they absorb as much carbon when the wood is growing as is released when it is burned, so biomass is considered to be carbon neutral. However, the initial installation cost of a biomass boiler is high and storage space for fuel needs to be considered.
  • Combined heat and power – some boilers have a separate engine within them that generates electricity when there is a demand for heat in the home. The cost of installation of combined heat and power boilers is very high and the government has withdrawn the feed-in tariff payment scheme.

Which boiler is right for my home?

When deciding what type of boiler you need, there are a number of points to consider, such as how much hot water do you require and how many bathrooms have you got.  Your Gas Safe registered installer is the best person to advise you; they will survey your property, look at the number of windows and the size of your rooms, identify the fabric of your walls and roof and recommend the correct output and type of boiler for your home using recognised industry calculations.

It is worth remembering that if a boiler is too small it will not be able to heat your home adequately or produce enough hot water. If it is too big, it will use more fuel than you really need, so your energy bills will be more expensive and your carbon emissions unnecessarily high.

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