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Gas Boilers: Explained

There are millions of gas boilers across the UK, which means there's a good chance you may have one in your home. However, how much do you actually know about your gas boiler?

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What is a gas boiler?

Gas boilers heat water in the same way as any other boiler, except they are powered by natural gas – they are the most common boiler that you find in UK homes. 

More eco-friendly alternatives are available to gas boilers, such as electric or biomass boilers.

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Are gas boilers being banned?

No, gas boilers are not being banned, but there are talks of natural gas being phased out for more environmentally friendly options. 

Burning fossil fuels, like the natural gas which is used in gas boilers, releases carbon into the atmosphere. With most UK households having gas boilers in their home, the impact we are having on the environment is significant. 

So, how can we reduce the environmental impact from gas boilers? 

One method could be hydrogen. When it’s burned, hydrogen doesn’t emit carbon into the atmosphere and it can be sent to your property through the existing gas network. However, it is unlikely 100% hydrogen boilers will be used in the near future. 

Instead, a hydrogen blend of natural gas and hydrogen will be delivered to UK homes. This will reduce the overall amount of carbon being released to the environment, therefore making it much more sustainable and environmentally friendly.  

You can read more about Hydrogen Boilers in our dedicated guide.


What is the lifespan of a gas boiler?

Usually, gas boilers will last between 10 and 15 years. However, how long you have your boiler for will depend on how well it is maintained. 

We recommend getting your boiler serviced annually so you can catch any potential issues early.

Want to keep your boiler in top condition?

Take a look at our pay monthly options and pick the best for you.

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Gas boiler types

There are three main types of gas boilers: combi, system and conventional. 


Combi gas boilers 

Combi boilers are one of the most popular heating systems in the UK. They are cost effective, compact and don’t need to be installed alongside any bulky tanks or cylinders. This makes them ideal for smaller properties with limited space. 

Everything a combi gas boiler needs to deliver hot water and heating is all in the boiler itself, which is why it is possible to deliver near-instant heating and hot water on demand. 


Conventional gas boilers

Conventional boilers are the oldest types of heating system, but technology has advanced over the years making them more efficient and more reliable than ever. 

In addition to the boiler, it needs to be installed alongside feed and expansion tanks as well as a hot water cylinder. Cold water fills the tank, often found in the loft, which is fed down to the boiler which heats the water before sending it to hot water outlets. 

A new conventional boiler should only be considered if your property already has one installed. They can be tricky to install and require extensive pipework. 


System gas boilers 

System boilers sit somewhere between a combi and conventional boiler in terms of how they work.

Like a combi boiler, they are directly connected to the mains, but they store hot water in a cylinder like a conventional boiler. This does mean that more space needs to be dedicated to the heating system, but it allows them to meet higher demands for domestic hot water. 

If you live in a property with 2 or more bathrooms, then a system gas boiler is likely to be the best option for you. 


Condensing gas boilers 

All boilers installed in the UK must now be condensing, and this has been the case since April 2005. 

Condensing boilers are fitted with a Flue Gas Recovery System, which allows them to hold onto more of the heat they make whilst burning. With non-condensing boilers, some of the heat goes straight out of the flue pipe and so is lost. 

A condensing boiler can make up to 30% more heat using the same amount of fuel compared to a non-condensing boiler. 


Modulating gas boilers

Most modern condensing boilers are able to modulate. This means their output rating can be lowered to run more efficiently. 

For example, a 30kW boiler with a modulation of 10:1 can also run at 3kW. This means the boiler will use less fuel when there’s a low demand for heating, which will save you money on your heating bills.

How do gas boilers work?

While there are a variety of boiler types, as discussed, they all work in the same way; by using gas as the fuel for your boiler which in turn heats your home and produces hot water.

The gas enters the boiler via two different methods:

  • By being connected to a main;
  • or through an LPG bottle.

The hot water produced by the gas boiler is then pumped through your central heating system, travelling through pipes into radiators to heat your home.

If you own a combi boiler, it will flow directly through taps and showers, whereas if you own a system or conventional boiler, the hot water will be transferred and stored in a separate water tank.

Man repairing a boiler

What is the most efficient type of gas boiler?

Gas boiler efficiency is based on their ERP rating, which allows you to see how energy efficient a product is. 

New condensing combi and system boilers are one of the most efficient types of gas boilers, with an ERP rating of A and an efficient output of at least 90%. 

These new efficient boilers are designed to last much longer, and could save you up to £500 on your heating bills thanks to the reduced loss of heat and energy. 


How much does a new gas boiler cost?

Including installation costs, a new gas boiler can cost anywhere from £1000 to £4000. Remember, this is just an average and costs could be higher than £4000. 

This is because there are a few factors which can affect the overall costs. These factors include:

  • The type of boiler 
  • Make and model 
  • If you are replacing a like-for-like boiler 
  • If the boiler is being moved
  • Rates charged by the installer 


Best gas boiler brands

There is a wide choice of gas boiler brands for you to choose from. Some of the top leading manufacturer include:

  • Baxi
  • Ideal
  • Worcester Bosch
  • Viessmann
  • Vaillant

Each manufacturer makes their own range of gas boilers, from combi to system, all of which come with long warranties. 


Do I need to get a gas boiler serviced?

Yes, your gas boiler should be serviced once a year to ensure everything is working as it should be. 

This will give you peace of mind knowing your heating system is running safely and efficiently. 

Our Gas Safe Registered engineers are fully qualified and can work on both Natural Gas and LPG boilers. You can find out more about our boiler service plans.

Does your Gas Boiler need servicing?

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Alternatives to gas boilers

While gas boilers have long been the solution to heating homes in the UK, there has been an increased demand for greener heating solutions which can lower household CO2 emissions. 

Below are the top alternatives to gas boilers. 


Electric boilers 

Electric boilers use electricity as the fuel, rather than gas or oil. By not burning any fuel, they are much safer than gas or oil boilers and are much less likely to run into a fault. 

However, they are unable to meet high demands of hot water or heating,which is why they are usually suited for smaller homes and flats. 


Oil or LPG Boilers

Oil and LPG boilers are similar to gas boilers, in that they use fossil fuels. However, oil and LPG can be stored on-site at your home or property. 

Being able to store these inexpensive fuels has become increasingly popular amongst off-grid homeowners. 


Biomass Boilers

Biomass boilers bridge the gap between alternative boiler types and renewable heating systems. They work the same way as gas boilers, but instead of burning gas they burn biomass; biological materials that come from plant based organisms. 

Whilst burning gas or oil produces carbon that is released into the atmosphere, burning biomass materials is a carbon neutral process. 

There are manually-fed or automatically-fed boilers, so if you choose manual, you will need to fill it with fuel when needed. Unfortunately, biomass boilers do require a lot of maintenance, much more than other heating systems. 


Air Source Heat Pumps

An air heat source pump extracts the warmth from the air outside, even when it is cold. This heat is then used to deliver heating and hot water in your home. 

Some models can even do so in temperatures as low as -25 degrees celsius.


Is a gas boiler better than electric?

Natural gas has proven to be a great fuel for heating our homes, but there is no hiding from the fact it has a negative impact on the environment.

For smaller bedroom flats and homes, electric boilers are a great alternative as they do not produce any emissions whilst heating the home. 

However, both gas and electric boilers have their pros and cons. Whilst electric boilers are much more environmentally friendly, they can be extremely expensive to run and cannot meet the heating demands of large properties. 

Gas boilers are much more affordable to run and can meet high demands for hot water, but they do have a risk of leaking carbon dioxide and require annual services. 


Should I choose a gas or an electric boiler?

Both gas and electric boilers are great for heating your home, however, which one you choose will depend on how efficient it will be in your home. 

Gas boilers are generally more efficient than electric boilers, especially if you have a home with multiple bathrooms and bedrooms. 

If you live in a small house or flat with one bathroom, an electric boiler may be the better option for you, as their outputs are usually too low for houses with multiple bedrooms and bathrooms. 


Should I replace my gas boiler?

There are a few different key indicators to look for when considering if you need to replace your gas boiler:

  • Your boiler is too old:
    Although it may be functioning as normal, if your boiler is around 10-15 years old, it may be time to replace it. Chances are your boiler will lose pressure every now and again. 

  • There are visible leaks:
    There are several reasons why your boiler may be leaking, including pressure valve faults, corrosion in the system, temperature valve issues and broken seals. 

  • Strange smells and/or noises:
    If your boiling is emitting strange smells or making strange noises, this may be a strong indication that something is wrong with your boiler internally and it should be replaced. 

  • Fluctuations in water pressure:
    When using taps in your home, such as the kitchen or bath tap, you may notice the water fluctuates in temperature. You may need to have your boiler re-pressurised, and if this doesn’t work, it should be replaced. 

FAQs about Gas Boilers

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