Boilers and Central Heating: The Ultimate Guide

By 12 min read

Learn about the different types of boiler and which one is right for your home.

Discover how a new A-rated boiler can save you up to £325 a year.

Fill out the form above to get a boiler quote from a trusted installer in your area.

Do you know your combi boilers from your condensing, your system boilers from your SEDBUK and your Viessmann from your Vaillant? We’re here to answer all your questions about installing, maintaining, replacing and repairing a boiler, starting with exactly how a boiler works.

A boiler provides your home with central heating and hot water. It does this by burning fuel, which heats both the water that comes out of your taps or the water which flows through your radiators and warms your rooms. The fuel it burns is usually gas from the mains, but you can also get boilers that run on oil, bottled gas or electricity.

Want to get straight to the point? Just pop your details in our short form, and a local installer will be in contact with you shortly.

a diagram showing how a new boiler can save you money

What's In This Guide to Boilers?

What Types of Boiler are There?

Different boilers work in different ways, and are suitable for different types of home. The law requires most new domestic gas boilers to be at least 88% efficient (86% for oil boilers), so you can be confident that any new boiler you choose these days will be economical.

The prices we’ve given are estimates and the ranges may seem wide, but this is because there are so many factors at play; both for the boiler itself and the installation, which may be very simple or very complicated. Some sellers may include installation in the price of the boiler – always check! The sure-fire way to get an accurate figure is to complete the form at the top of this page to hear from our trusted suppliers.

Combi Boilers

Combi boilers are the most popular kind of new boiler in the UK, because they provide instant, unlimited hot water. They don’t have a hot water tank or cylinder, which saves you space; they heat the water as you need it. But, they don’t always cope well in big houses where lots of people need hot water at the same time.

Cost: £500 to £3,000 or more

Installation cost: £500 to £2,200 or more

Conventional Boilers

Conventional boilers have a hot water tank in the loft, and a hot water cylinder, usually in the airing cupboard. This takes up more space and means you don’t have hot water on demand – you have to heat it up. But it does mean you can run the hot water in different places at the same time, which is pretty important if you have a big household. Older conventional boilers are often not that efficient, you’ll notice a big difference with newer models.

Cost: £500 to £2,000

Installation cost: £600 to £2,000 or more

System Boilers

System boilers are similar to conventional boilers, but there’s no hot water tank in the loft, just a hot water cylinder. This frees up your loft space, and also makes installation simpler. As with a conventional boiler, you can supply hot water to several taps at one time, but the hot water can run out. Solar panels are much more easily compatible with a system or conventional boiler than a combi boiler.

Cost: £500 to £2,000

Installation cost: £600 to £1,100 or more

Oil Boilers

Oil boilers are an alternative to gas, particularly for homes which aren’t connected to the mains gas supply. You’ll need to have your oil delivered and stored in a tank.

Cost: £900 to £3,000

Installation cost: £700 to £2,000

Megaflow Cylinders

Megaflow boilers or cylinders are suited to houses with several bathrooms where several people are likely to be using the hot water at a time. They can run off your electricity supply, which means they’re suitable for homes not connected to mains gas – this also means you can have hot water even if your boiler breaks. Megaflow cylinders can also be connected to solar panels. However, although they don’t require a cold water tank, they tend to be bulky, and if the hot water runs out, you’ll need to wait for it to heat up again.

Cost: £600 to £2,000 or more

Installation cost: £500 to £1,500 or more

There are also biomass boilers, which are wood-fuelled heating systems; you can read about biomass boiler costs here.

Why Get a New Boiler?

Besides the obvious (it’s broken), here are some reasons why it might make sense for you to upgrade your boiler:

Cost savings: If your boiler is very old, it could be hopelessly inefficient by modern standards. All new domestic gas boilers in the UK have to be at least 88% efficient, whereas some older boilers are only around 55% efficient. This means that for every £100 you spend on heating and hot water, up to £45 is wasted.

The Government’s official figure is that you could save up to £325 a year if you replace a G-rated boiler with an A-rated boiler – i.e. replace an extremely inefficient old boiler with a tip-top new one. But that figure is for a family of 4 living in a semi-detached house. If your home is smaller, or your boiler is reasonably efficient, the savings aren’t going to be as dramatic.

Environmental impact: Inefficient boilers don’t just waste your money, but the earth’s natural resources too. A more efficient boiler will reduce your carbon footprint.

How do you know how energy efficient your boiler is?

A boiler’s ErP rating and SEDBUK rating tell you how efficient it is. ErP ratings go from G (the lowest) to A+++ (the highest). Most new boilers have an A rating or above.

Reliability: As with everything, as a boiler gets older, you can expect it to have more problems – and it may become harder to source the parts you need to repair it. The expense of this is bad enough, but pales into insignificance next to the pain of having no heating or hot water if it breaks down in winter.

Space: If you swap a conventional boiler with a hot tank and water cylinder for a combi boiler, which requires neither, you’ll free up space in both your airing cupboard and your loft.

When Should You Replace an Old Boiler?

As a general rule, the lifespan of a boiler is around 12 to 15 years. But if yours is 15 years old and you still feel it’s working fine and your heating bills aren’t enormous, then you may want to let sleeping boilers lie for the moment. If it starts to break down a lot, or your home always feels cold, or your energy bills are massive, or you’re having trouble getting the parts it needs, those are all signs that it’s on its way out. Check out our page on how often a boiler should be replaced for more information.

Could You Save With A New Boiler?
Select How Many Live In Your House To Find Out!

Boiler House

Here are a few things to think about when choosing a boiler:

Type: You’ll want to think about whether you want a combi, conventional or system boiler. If you have a small home where space is at a premium, you’ll probably want a combi; a conventional boiler might be better suited to a large family.

Capacity: A bigger home will generally require a more powerful boiler, because it will have more work to do. You need to get the right capacity boiler for your home; a boiler that isn’t powerful enough won’t give you enough heat, but a boiler that’s too powerful just overheats your home and wastes your money.

Efficiency: Obviously the more efficient the boiler, the better, but there’s little to choose between modern boilers in terms of efficiency.

Warranty and reliability: You’ve probably got better things to do with the money you’ve saved on your heating bills than spend it calling out an engineer. And if you do have to have your boiler fixed, you want spare parts to be easy to get hold of.

Fuel type: If you’re not connected to mains gas, it’s usually possible to get connected if you want a gas boiler. Oil and electricity both have their advantages and disadvantages too.

Size: Where do you want your boiler to go, and will it fit in that space? Do you want a wall-mounted or floor-mounted boiler? Some modern boilers are small enough to fit in a kitchen cupboard.

What Size Boiler Do You Need?

To answer this question accurately, it’s best to discuss it with a heating engineer.

As a rough guide, these are the figures for combi boilers:

For a 1 or 2-bedroom house with 1 bathroom: 24 to 27kW

For a 3 or 4-bedroom house with 1 or 2 bathrooms: 28 to 34kW

Anything bigger: 35 to 42kW

These figures are a rough guide for a conventional boiler:

1-bedroom flat: From 12kW

2 or 3-bedroom flat or house: 15kW to 18kW

4 or more bedrooms: 24kW to 30kW

The answer will be affected by a number of factors, such as how many radiators you need to heat, how well insulated your home is, how many bathrooms you have, the size of your rooms, the height of your ceilings, how many external walls you have or what floor you’re on.

Here, Francis, a Gas Safe registered boiler engineer, explains why it's so important that you get the right sized boiler for your home.

Complete the form at the top of this page to get a free quote from one of our suppliers who’ll be able to advise you on the best option for your home.

How Much Will a New Boiler Cost?

Boiler prices start at around the £400 mark for a small electric boiler or between £400 and £500 for a small gas combi, and go all the way up to several thousand pounds for some pretty mighty models. The price will depend on factors including the supplier, the type of boiler and its capacity.

You may also be able to buy your boiler on finance, i.e. pay for it in monthly instalments. Be aware, though, that this is a loan, so you must be sure that you can keep up the repayments. Some finance agreements are interest-free, but interest payments can increase the overall cost hugely.

Hit the button below to get an accurate price, including installation, from our suppliers or read more about boiler costs.

Which Boiler Brands are Best?

As with many things, the best brands are generally established household names who have fine-tuned the art of boiler building over many years. Here are some of the top brands based on our own experience and reviews from customers and engineers:

Boiler Brand
Worcester Bosch
Worcester Bosch is one of the UK's top boiler brands, with a 5-star rating on the Trustpilot.
Viessmann produce highly efficient boilers that make minimal noise. The brand has a 4.5 star Trustpilot rating.
Vaillant have been building affordable boilers for over 100 years, earning a 4-star Trustpilot rating.

Traditional British brands Ideal, Grant and Baxi are considered trustworthy and reliable, and all new Baxi boilers are endorsed by the Energy Saving Trust. Other well-known brands include Alpha, Potterton, Glow-worm, Vokera, Johnson & Starley and Intergas.

Read our best boilers guide to get the full lowdown on leading manufacturers.

Boiler Servicing and Repairs

boiler servicingYou should have your gas boiler serviced every year by a registered Gas Safe Engineer. Gas appliances which aren’t working properly can emit carbon monoxide, a poisonous gas which can kill you or cause long-term damage to your health. You can’t smell or see carbon monoxide, so we also advise putting a carbon monoxide detector near the boiler for added protection.

There are other important reasons to have your boiler serviced annually. It makes sure it’s not costing you more than it should by working inefficiently. It allows you to nip in the bud minor problems that might become major, and majorly expensive, later on. And your warranty, and any home insurance that you have concerning the boiler, might also become invalid if you don’t keep up with the servicing.

For oil boilers, OFTEC, the oil heating industry’s trade association, advises either an annual service or whatever your manufacturer recommends. All the reasons above apply to oil boilers, including the risk of carbon monoxide poisoning.

Electric boilers don’t need so much maintenance, as there isn’t the risk of carbon monoxide poisoning. We’d advise following whatever your manufacturer recommends.

How Much Should It Cost to Have Your Boiler Serviced?

For gas boilers, prices range from around £50 to just under £100 for a standard service.

For oil boilers, prices can be a bit more expensive, sometimes going up to almost £200, although the quotes we got for a home in the south east of England ranged between £65 and £100.

There’s more in-depth information about prices on our boiler servicing costs page.

How Much Will It Cost to Repair Your Boiler?

It depends what’s wrong with it, what part of the country you live in, how old your boiler is and when you call the engineer out. As a rough estimate, you would probably be looking at somewhere between £100 and £400 for most repairs, including parts and labour.

Take a look at: Boiler Repair Costs

What's next?

Now that your boiler knowledge is in tip top condition, enter your details on our short form, and a local installer will be in contact with you shortly.

Amy Catlow
Amy Catlow Publishing Director

As the self-proclaimed ‘Queen of Green’ Amy has been an environmental evangelist for as long as she can remember. Whether it’s crunching the data or helping visualise it, Amy has the nous to help you turn your home into an money saving eco-fortress.