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Gas Boilers Advice & FAQs

Gas Boilers Advice & FAQs

All You Need to Know About Gas Boilers & Central Heating

Gas boilers are found in almost every home and workplace, so you’d think we would have a better idea of how our central heating systems work. In fact, while we rely on boilers to reliably heat our properties and supply us with hot water, the big white box that’s often found hidden away in a cupboard remains something of a mystery to many.We’ve answered a variety of questions about gas boilers, from their internal components and safety features, to their life expectancy and how to find the best model for your home - whether that's a combi, system or heat only boiler.Whether you want to know how they work or find out if it’s time to upgrade, here’s everything you need to know about gas boilers…

What is a Gas Boiler?

Essentially, a boiler is like a big furnace or fire that’s controlled by your thermostat. The main function of a gas boiler is to act as a heater and provide buildings with the hot water they need, which is important for two very big reasons.

Firstly, the hot water produced by your boiler is pumped through your radiators when you turn on your central heating, providing them with a reliable source of heat. This keeps you warm and comfortable in the colder months of autumn and winter — and sometimes during spring and summer as well.

The second main function is providing a steady supply of hot water for your sinks, baths and showers. They do this by heating up a tank or container of water and keeping it at a consistent temperature, which means you can rely on the hot water you need to keep yourself (and your belongings) sparkling clean.

How Does a Gas Boiler Work?

While there are a variety of gas boilers on the market, they all work in much the same way — by heating gas to warm your home. This gas can enter the boiler via two different methods: by being connected to a main or through an LPG bottle.

The hot water produced by your gas boiler is then pumped through your central heating system, travelling via pipes into your radiators to heat your home. Depending on the type of boiler you own, this will either flow directly through taps and showers (combi), or will be transferred and stored in a separate water tank or cylinder (system and heat only).

What Does a Gas Boiler Do? Central Heating

Central heating works like a circuit – hot water is pumped from the boiler into each radiator in turn, and is in constant, or near-constant, circulation when the heating is switched on. Although you might need to top up the pressure in your radiators from time to time, the same water is used over and over again. 

By the time the water has passed through all the radiators, it will have lost some of its heat, but that is restored in the boiler and it is sent around again.

Whether or not central heating is “on” is determined by the thermostat, which helps the temperature of a home stay more or less constant, to within a few degrees either side of your chosen temperature.

What Does a Gas Boiler Do? Hot Water

The second job of the gas boiler is to heat water. It performs this task in the same way as it does for central heating, that is, through pumping circulated water over the flame so it heats up.

There are two ways it does this:

1. Instant hot water as in the case of the combi boiler

2. Heating water in a tank, like the system boiler or the heat only boiler

In both cases, however, the water that is heated over the flame is not the water that comes out of the tap – it is simply used as a medium for heating the water you use.

What’s Inside a Gas Boiler and How Does it Heat Water?

There are numerous components housed inside a gas boiler, including a gas burner, heat exchanger and a flue. Each element serves a specific purpose, working together to keep your home warm and provide you with a continuous, reliable supply of hot water.

Below are the main individual components, along with the functions they fulfill:

  • A valve allows gas to enter the combustion chamber

  • The gas burner works exactly how it sounds, by burning gas to produce the heat that’s required for your home and hot water

  • The heat exchanger safely transfers heat to the water by passing it through a pipe within the heated gas chamber

  • A pump or fan pushes this water out of the boiler and either into the system or a separate cylinder or storage tank

  • A flue or waste pipe connects your boiler to an external part of your property. It is responsible for safely releasing the by-products produced by your boiler, including water vapour and carbon monoxide.

central control board allows you to control your boiler

Do Gas Boilers Need Electricity?

Although it’s gas that heats the water in our boilers and keeps our homes warm, gas boilers actually do need a small amount of electricity to work too. That may sound strange, but electricity is simply used to help specific parts and mechanisms of our central heating systems function.

Electricity is used to power everything from the valve that opens to let gas flow into the combustion chamber, all the way to digital displays and smart thermostats like Ideal’s app-controlled Halo system.

How Do Combi Boilers Work?

Combi boilers are suitable for most small and average-sized households. They work by circulating hot water around the central heating system, and also heat up incoming mains water incredibly quickly when a hot tap is turned on. That means instant hot water, 24/7. They don't require storage tanks either, which means they take up hardly any space. 

A potential drawback is that if several people turn on different hot taps or showers at the same time, pressure and temperature of the water will drop as the heating capacity is exceeded. Also, since they rely on water mains pressure, they are unsuitable for areas of low pressure.

How Do Heat Only Boilers Work?

Also known as conventional, regular, open vent or traditional boilers, these systems heat water that circulates around the central heating system; a separate circuit heats up a hot water tank, warming up the water in the tank. The tank is fed by a cold water tank, usually in the loft, which is fed by mains water. This is the traditional type of boiler used in all homes before the 1970s.

Heat only boilers are useful for larger households, because once the tank is full of hot water, multiple taps can be run from them at the same time. The hot water tank can have electric elements installed to heat the water overnight when electricity is cheaper, or to act as a backup should the boiler break down. The main drawback is that once the hot water is used up (i.e. if someone has a deep bath), everyone has to wait for the water to re-heat again. They can also heat more water than is required, which is inefficient. 

How Do System Boilers Work?

System boilers are similar to heat only boilers; the main difference is that the hot water tank is fed by mains water, not water from a cold tank. They therefore use up less space, but have the same advantages and drawbacks as heat only systems.

How Long do Gas Boilers Last?

How long a gas boiler lasts depends on how well it’s cared for, but it’s generally best to replace it every 15 years. It’s not that they’ll suddenly stop working at this age, but this is the point where it becomes more cost effective to invest in a new model.

Gas boilers are complicated appliances that work around the clock to make sure we have hot water and heating, whenever we may need them. They work so hard to keep us comfortable that even the most reliable boiler parts will eventually fail.

Here at Ideal, our gas boilers come with warranties of up to 12 years. Simply register your warranty within 30 days — your installer may do this for you — to enjoy continual support and peace of mind.

Signs You May Need a New Gas Boiler

There are several signs to be aware of that may signal your trusty gas boiler is reaching the end of the road. It may be regularly breaking down or losing pressure, or you may notice unusual loud bangs coming from your central heating.

If your gas bills start to creep up unexpectedly, that’s another sign that your boiler is not operating efficiently. In all of these cases, we’d recommend calling out a Gas Safe engineer to cast an expert eye over it. It could be that there’s a simple solution, or they may advise you it’s time to invest in a new model.

For more information, visit our blog post on replacing an old boiler.

How to Look After a Gas Boiler

Our faithful gas boilers can’t last forever, but there are steps we can take to look after and keep them working as efficiently as possible. Annual services performed by a Gas Safe accredited engineer will include essential safety checks and ensure all of its parts are working as they should.

Other top tips for keeping your gas boiler healthy are running it for around 15 minutes even in the summer months. It’s also good practice to keep an eye on your boiler’s pressure to make sure it doesn’t get too low, and try bleeding your radiators if they seem cooler at the bottom.

Not only will your gas boiler last longer if you take good care of it, that extra efficiency will also mean your utility bills stay lower. It will also benefit the environment, as it won’t need to work quite so hard to keep your home warm.

Do I Always Need to Get my Boiler Serviced?

To ensure your gas boiler remains safe, you need to book a service with a qualified Gas Safe engineer. This should be completed on an annual basis in order to keep your boiler in good repair, ensure it remains efficient and to comply with your warranty.

Neglecting your annual service may void your warranty, which could leave you with an expensive bill if any work is required. You can read more about boiler servicing, including what it involves and how to prepare, in our servicing guide.

We also recommend installing a carbon monoxide detector. This will alert you to the presence of this toxic gas and provide you with peace of mind. If you live in a rental property, your landlord is required to install carbon monoxide detectors and they must be in place from the day your tenancy starts — read our guide to find out more about your rights as a tenant.

Are Gas Boilers Efficient?

When it comes to gas boiler efficiency, the ErP (Energy-related Products) Directive uses ratings between A+++ (high performance) and G (low performance) to rank different models. These ratings consider how effectively a boiler converts a fuel source into heat and how much heat is lost or ‘wasted’ in the process.

Any appliance that heats water and spaces, including gas boilers, must have an energy label that displays its ErP rating.

You’ll find the ratings for all of our Ideal boilers displayed prominently on each product page, such as the Vogue Gn 2 Combi. You’ll also find a copy of each model’s ErP label under the section marked ‘Downloads’ on the same page.

Here at Ideal, we’re proud to manufacture some of the UK’s most efficient gas boilers. For more than 100 years, we’ve worked hard to devise and incorporate the latest technology, and today, all of our new gas boilers are A-rated.

Are Gas Boilers Safe?

The short answer is yes. Modern gas boilers have been created with technology that has specifically been designed to keep you, your family and your home safe. This is thanks to the development of new safety features, including a sealed or balanced flue.

Older models were typically constructed with an open flue or chimney. These systems worked by drawing in carbon dioxide from the room, the gas was then combusted, and wasted products were ejected outside. However, an open flue can be subject to a range of issues, including blockage.

When a flue becomes obstructed, this can cause the boiler to release carbon monoxide into the home, which is a colourless, odourless and tasteless gas. High levels of carbon monoxide can have negative impacts on health — take a look at our blog post protect your family from CO for more information.

Today, modern gas boilers are manufactured with a balanced or sealed flue. Connecting your boiler to the exterior of your home, this type of flue works by drawing in carbon dioxide from outside, heating and then drawing the waste back out. Unlike an open flue, the air inside your boiler is sealed off from the room where it’s housed, meaning toxic gases are unable to escape.

Read our boiler flues guide to find out how this component works.

Should I Be Able to Smell Gas from my Boiler?

When working correctly, your boiler should be quiet, run efficiently and emit no odour. If you can smell gas, this could be caused by issues such as a buildup of bacteria or dust, corroded pipes, or overheating, all of which can cause a gas leak.

So, what should you do if your boiler smells of gas?

If you smell gas, notice a rotten egg smell coming from your boiler, or suspect a gas leak, this should be considered an emergency situation. As such, there are several steps you need to take:

  • Evacuate the property and ensure that no one is in danger

  • Call the National Gas Emergency line on 0800 111 999

  • If you’re able to, switch off your gas supply — the valve is usually located in the meter box

  • Open all doors and windows to allow air to circulate

  • Don’t touch any outputs, switches or devices that are connected to the electrics — there’s the risk of a spark

  • Don’t light matches, candles or smoke

  • Don’t use your mobile phone inside or near the property

  • If you feel ill, seek immediate medical treatment

In this situation, it’s crucial that you don’t reenter the property until you’ve been advised that it’s safe to do so by a Gas Safe engineer.

Should I Buy a Gas Boiler?

If you’re looking to heat your home in a safe and cost effective way, buying a gas boiler could be the right choice. Available in a range of types, sizes and wattages, there are models to suit all properties, from small flats to large family homes.

The cost and time required to install a gas boiler can vary, depending on the model chosen and the amount of work that’s required. However, it’s important to remember that mains gas remains one of the cheapest fuel options available in the UK.

This is where choosing a new, highly efficient model can pay for itself. With less wastage, a modern gas boiler could lower your energy bills, keeping your home warm and your water heated at a cheaper price.

Should I Choose a Gas or Electric Boiler?

When deciding whether an electric or gas boiler would be better suited to your home, consider fuel type and long-term costs. This includes if your property is connected to the gas network and factoring in not only the price of installation, but your ongoing energy costs.

While the majority of homes in the UK are installed with gas boilers, there is another option: electric. An electric boiler can be a feasible option in a property where there’s no gas available, as they provide heating and hot water without having to be connected to a mains.

However, while electric boilers are often cheaper to buy and install, they can cost significantly more to run than gas boilers. On average, a kW of electric costs three times the amount of a kW of gas, which can lead to much higher energy bills.

Can I Run a Boiler on LPG Gas?

While the majority of UK properties are connected to mains gas, there are approximately four million homes that remain unconnected to the network. If you live in one of these properties, running your boiler on LPG gas could be the ideal central heating solution.

An LPG boiler runs on Liquid Petroleum Gas and operates in much the same way as a standard gas boiler. The key difference here is that instead of sourcing gas directly from the mains, an LPG boiler is connected to a storage tank.

Rather than paying your monthly gas bills directly to a supplier, LPG gas must be bought in advance and stored outside your property. A qualified gas engineer will be able to advise you on the process, from the size of the tank required and its location, to ensuring there’s adequate spacing and airflow.

Additionally, it’s possible to convert a standard gas boiler to LPG. Here at Ideal, we have LPG conversion kits available for all outputs, including some of our most popular Logic and Vogue models. To find out more, speak to a Max Accredited Installer.

Where Can I Put My Gas Boiler?

Whether it’s under the stairs, in the bathroom or in your kitchen, there are plenty of options available when it comes to siting your gas boiler. In older properties, boilers are commonly installed in a hallway or bedroom cupboard, while modern, compact models can be housed in more places.

Before you make a decision, there are some key practical considerations to bear in mind, including:

  • Making sure there’s plenty of space available for servicing and maintenance.

  • Taking fire safety standards into account.

  • Observing the manufacturer's instructions around ventilation

  • Meeting IEE Wiring Regulations, so there’s no risk of your boiler being accidentally splashed with water

Modern gas boilers are much quieter than older appliances — especially models like the Logic+ combiLogic+system and Logic+heat only, which have been awarded with the Quiet Mark. We are getting closer, but gas boilers still don’t run silently, so you may want to find a location where you won’t notice any noise.

If you’re thinking of housing your gas boiler in a specially fitted cupboard, we’d recommend browsing our guide to kitchen suppliers and boiler cupboard dimensions.

How Do I Choose a Gas Boiler?

With so many models on the market, you may be unsure how to choose a gas boiler. That’s why we created our helpful product selector tool, to take the guesswork out of choosing your gas central heating boiler and provide you with a selection of suitable models.

To Find Your New Boiler, simply follow this easy step-by-step process. Select your property type; number of bedrooms, bathtubs and showers; the type of boiler required; and the fuel used. Based on your selections, you’ll receive a list of boilers that could fit your needs.

The Best Gas Boiler for my Property

The best gas boiler will be different for every property. This depends on a number of factors including the size of your home; the type of fuel required; how many baths and showers there are; and the type of system you already have installed (e.g. combi or heat only).

As a general rule of thumb, we recommend the models below:*

  • For a one-bedroom flat, our Logic Max Combi could be an ideal fit. This flexible boiler can be connected to the mains or run off LPG.

  • For a three-bedroom house that requires a system boiler, our Vogue Max System is capable of providing the power a family may need.

  • For a four-bedroom detached home, the durable Logic Max Heat can power several showers at once, making it perfect for larger households.

*This should be considered as guidance only. We always advise speaking to a professional heating installer to clarify the best option for your home.

For more guidance on finding the best boiler for your home, take a look at our boiler size blog post.

What is a Condensing Boiler?

In the past, the flames would do their work on the water in the pipes, but then the heat from the flames would be vented to the atmosphere. Considering this could be at more than 200°C, that’s a lot of wasted energy.

What condensing boilers do is effectively use the heat twice. First, the flame heats up the water in the pipes and the water is sent on its way to the radiators, tank or taps. But then the hot air and flue gases pass through a series of baffles, where they pass around piped cold water coming in the opposite direction. The cold water therefore starts to get heated up before it arrives at the flames.

That means that less heat energy – and therefore less gas – is needed to heat the water up to its operating temperature.

All new boilers are required by law to be condensing boilers, and this law came into effect for gas boilers in 2005 (or 2007 for oil boilers). So if your boiler is newer than that, it should already be a condensing boiler.

Will Gas Boilers be Replaced in 2025?

You may have heard the government is planning to introduce new legislation around the future of heating systems in the UK. The Future Homes Standard will include new rules for new build homes, which means they’ll use alternatives to gas for their heating systems beginning in 2025.

This certainly doesn’t mean that gas boilers will disappear or be banned, as the legislation only applies to new build homes. There’ll still be many efficient gas boilers continuing to heat homes and workplaces in 2025 and beyond, working alongside alternative heating systems to lower carbon emissions for all of us.

Alternatives to Gas Fuel for Boilers

Four million of the UK’s 24 million homes are heated by fuels other than gas. Electric boilers make up a significant minority in the UK, accounting for about 1.7 million homes.

Out in the countryside or in other remote areas, it’s still quite common for houses not to be connected to the gas mains. These homes will usually have boilers fuelled by bottled gas or oil, which needs to be delivered and stored safely. In rare cases, boilers can even be powered by coal or wood.

Terminology Breakdown

ErP Rating

The energy efficiency of products is measured using the ErP (Energy-related Products) Directive. It helps us understand how efficient appliances that use energy are before we decide to make a purchase.

For gas boilers, the ratings scale runs from A+++ to G.

Gas Safe Accreditation

The Gas Safe Register is the official list of businesses and engineers qualified to legally work on gas appliances in the UK, Isle of Man and Guernsey.

Only gas engineers who are fully qualified and able to demonstrate their experience and competence can join the register.


Liquefied petroleum gas (LPG) is a hydrocarbon gas, most often propane and butane, which is stored as a liquid to be used as a fuel source.

Max Accredited Installer

Ideal’s very own Max Accredited Scheme provides installers with additional training. This means they can fit products from our Logic Max Range to the highest standards and offer homeowners extended warranties.

Wattage /kW

A kW, or kilowatt, is a measure of power that is equal to 1,000 watts. To put is simply, boilers with a higher wattage are able to provide more hot water to your home at any one time.