Replacing a boiler – everything you need to know

When replacing a boiler is on the agenda, this is what you should be aware of

Gas boiler on blue wall
(Image credit: natatravel Getty Images Creative #: 1247940293)

You might be thinking about replacing a boiler if your existing model is old and inefficient. Or perhaps replacement is an issue because it doesn’t provide sufficient hot water when family members all hit the shower at once in different bathrooms. Alternatively, you could be extending your home and need a new boiler that will cope with the extra load.

Whatever the case, you’ll want to know what the process of replacing a boiler that’s part of your home heating system consists of, what should be considered when you’re doing so, and who should do the work – and everything you need is here along with advice from the experts. 

And while the majority of British homes will be contemplating replacing a gas boiler, if yours runs on oil we’ll let you know whom you should call on for that, too.

When is replacing a boiler necessary?

When might replacing a boiler be necessary? It can be a good idea if your boiler is more than 10 years old. 

‘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 per cent more efficient than the older models,’ says Chris Riley, national operations manager for Baxi.

Replacing an old boiler can therefore mean your boiler uses less fuel, saving you money, plus reducing your carbon emissions.

But, if you inherited the boiler when you moved into your home, you might not know if it is an old non-condensing model. Chris says you can tell if it’s a non-condensing model if: 

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,’ he continues, ‘then you have a standard efficiency boiler and could save up to £305 a year by replacing it with a high efficiency model.’

Other circumstances in which you might be replacing a gas boiler include when it’s broken down and, in consultation with your heating professional, you decide replacement is a better strategy than costly repairs. 

Bear in mind, too, that if you are extending your home, replacement can be necessary because the boiler will not cope with the additional load. If the boiler is adequately sized, relocating it may be required in the new layout and in that case a newish model will be worth moving, while an older version might be better replaced.

Is it easy to replace a boiler?

The job of replacing a boiler can be straightforward, but it’s essential to call on the right professional. ‘Modern heating systems can be complex and sophisticated, and because every home is slightly different we always recommend speaking to a qualified heating installer,’ says Martyn Bridges, director of technical communication & product management at Worcester Bosch. ‘Any installer needs to be Gas Safe Registered and for peace of mind they must carry a Gas Safe Register ID card, which you should ask to see when they arrive.’

Not replacing a gas boiler but an oil-fired model instead? Then it’s an OFTEC registered installer you need.

There are three main types of boiler, and the simplest replacement will be for a boiler of the same type be that a combi, system, or regular (aka a heat-only or traditional) boiler.

‘When it comes to replacing traditional boilers, often the easiest thing to do is replace like for like but, if you have a water tank in your loft and you wish to free up that space, you can opt to change the cylinder from a vented to an unvented version (which does not require loft tanks), or even convert to a combi boiler,’ explains Darran Smith, Technical Manager for Alpha Heating Innovation. ‘However, you will also need to bear in mind the extra expense of making changes to an existing system.’

What is the process of replacing a boiler?

It’s important to have a home survey by your registered installer first when you are replacing a boiler. Your chosen professional will check your home’s construction materials, the size of the rooms, and the number of windows in order to recommend the right type of boiler and the output it should have. 

When it comes to the day of installation, there are a number of steps, as Matthew Jenkins, heating expert at MyJobQuote, explains:

1. The removal of the old boiler will be the first task. The length of time it takes to remove the old boiler will depend on the existing system. 

2. Depending on the state of the system, a power flush may be required. 

3. Your pipes may need to be changed or upgraded due to the installation of your new boiler. 

4. Your new boiler will be installed either in the same place as your existing boiler or in a new location, depending on your preferences and the type of boiler you choose. 

5. A system filter should then be installed. The system filter keeps your boiler as efficient and clean as possible. 

6. Your installer will commission the system once your new boiler is fully fitted to check everything is working properly. 

7. The boiler will then be registered with the boiler manufacturer by either the homeowner or the installer for the warranty to be effective.

How long does replacing a boiler take?

The length of time replacing a boiler takes depends on the extent of the work. ‘If you are simply having a like-for-like replacement boiler installed, then your engineer will usually have all the work wrapped up within one working day,’ says Darran Smith.

‘Should the work be a little more complex, for example if the old pipework is not fully compatible with your new boiler, you should expect the job to take one and a half to two days. 

‘Scenarios that involve moving a boiler much further away from the current position, fitting a different type of boiler or power flushing your heating system will require more time and you will find the process could take up to three days.

‘I’d then suggest asking for a little time with the engineer once the installation work is done and dusted so they can take you through the new boiler controls.’

Sarah Warwick
Freelance Editor

Sarah is a freelance journalist and editor writing for websites, national newspapers, and magazines. She’s spent most of her journalistic career specialising in homes – long enough to see fridges become smart, decorating fashions embrace both minimalism and maximalism, and interiors that blur the indoor/outdoor link become a must-have. She loves testing the latest home appliances, revealing the trends in furnishings and fittings for every room, and investigating the benefits, costs and practicalities of home improvement. It's no big surprise that she likes to put what she writes about into practice, and is a serial house revamper. For, Sarah reviews coffee machines and vacuum cleaners, taking them through their paces at home to give us an honest, real life review and comparison of every model.