Different types of boiler systems – the best for your home

There are different types of boiler systems available: combi, system and regular boilers. Find the best one for your home.

Boiler on wall in kitchen
(Image credit: Heatable)

Which you choose from the different types of boiler available is crucial. The different types are suitable for different sized homes and different household needs, so you’ll want to be in the know when the time comes to fit a new one, as well as in order to understand how your current boiler works.

A large majority of British homes have a gas boiler as part of a home heating system, providing the hot water for the radiators that heat your rooms and to taps, so knowing how to keep your boiler working safely is key to making your home warm and comfortable.

Our guide has all you need to know about the various types of boiler on offer plus the maintenance they need to keep working safely and efficiently, and we’ve got advice from the experts, too, so you can be sure you’re boiler savvy. 

What are the three different types of boiler?

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There are three main types of boiler: combination boilers, generally known as combi boilers; system boilers; and regular boilers, also called heat-only boilers. Which is the best for your home will depend on its size, needs and the current heating system.

Combi boilers

Combi (combination) boilers are the UK’s most common boiler type. They provide near instantaneous hot water on demand and require no external tanks or cylinders. ‘Request hot water from your taps and it is with you in seconds with a combi boiler,’ says Sam Rigby, from Heatable

Additionally, there are also some storage combi boilers on the market, from companies including Viessmann and Valliant, which have a built-in storage tank for hot water.

‘A combi boiler is perfect for smaller properties with little or no loft space, thanks to the fact there isn’t a need for a hot water cylinder,’ says Martyn Bridges, director of technical communication & product management at Worcester Bosch

‘They are also very cost effective and energy efficient as water is heated instantly rather than being heated and stored in a cylinder. An added benefit is that hot water is delivered at mains pressure, meaning a powerful shower.’

The timing of each person’s bathing matters if you’re considering a combi. ‘They are not suitable for homes with more than bathroom used at the same time,’ says Chris Riley, national operations manager for Baxi.

System boilers

System boilers provide both central heating and hot water, but they do require a hot water cylinder for storage, which will take up extra space. ‘However, the main heating and hot water components are built into the boiler itself, making it quicker and easier to install,’ explains Martyn Bridges.

‘These boilers are compatible with solar water heating systems, which deliver environmental benefits as well as lower energy bills,’ he adds.

If your home has more than one bathroom and these are being used at the same time, a system boiler can suit. ‘System boilers can be a great option for households demanding a lot of hot water at any one time, but the hot water isn’t instant and will require potentially up to an hour (depending on boiler and cylinder size) to heat,’ adds Sam.

Regular, heat-only boilers

Regular or heat-only boilers are seen in most older UK heating systems. ‘Heat-only boilers are also known as regular, traditional, conditional or open vent boilers,’ says Chris Riley. ‘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.’

‘Water from the tank is gravity-fed to the system below, usually resulting in a much lower water pressure,’ says Sam.

The pros and cons? ‘They are slightly less efficient than combis, but they are the go-to choice for large homes with a high demand for hot water or multiple bathrooms, or for situations that already have a traditional heating and hot water system in place,’ says Darran Smith, technical manager for Alpha Heating Innovation.  ‘On the downside, they tend to be more expensive to install and take up more space.’

Bear these issues in mind, too. ‘You need to wait for the water in the cylinder to heat up before you can use it, and tanks in the loft could be susceptible to freezing,’ says Chris Riley.

Alternative boiler options

If you don’t have mains gas, boilers fuelled by oil are an alternative. And there are other less common types of boiler, too, including electric, solid fuel or biomass, and combined heat and power.

‘Electric boilers are much more energy efficient than gas boilers, but electricity is more expensive to buy,’ says Baxi’s Chris Riley. ‘They do not have a flue, so are more suitable for homes where a flue is not an option, such as tower blocks.’

Why might you consider 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,’ says Chris. ‘However, the initial installation cost of a biomass boiler is high and storage space for fuel needs to be considered.’

Combined heat and power boilers are also available. ‘These have a separate engine within them that generates electricity when there is a demand for heat in the home,’ explains Chris. ‘The cost of installation of combined heat and power boilers is very high and the government has withdrawn the feed-in tariff payment scheme.’

What is a condensing boiler?

A condensing boiler isn’t a type of boiler, but it is important to be aware of what one of these is.

‘The term “condensing” refers to the technology inside the boiler rather than the actual boiler type,’ explains Chris Riley. ‘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.

‘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.’

What type of boiler is best?

The type of boiler which is best will depend on your home’s size, and its rooms, as well as your household’s requirements. 

‘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,’ says Chris Riley. ‘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.’

Why replace your boiler?

If your boiler is more than 10 years old, it’s probably not doing the job it should be anymore. 

The boiler installation experts at Heatable say replacing a very old boiler with a modern combi boiler could save you up to £400 a year on your energy bills. More standard boiler replacements will offer savings between £40 and £100 a year, which soon adds up.

If you’re planning an extension or loft conversion, the extra load that’s going to be put on your boiler – even if it is more modern – means replacement needs consideration. Your current model may not be up the job.

Get a quote for a boiler replacement

You should always use a heating engineer who is a registered installer to fit a new gas boiler. Gas and LPG boilers should be fitted by someone who is Gas Safe registered. ‘For peace of mind they must carry a Gas Safe Register ID card, which you should ask to see when they arrive,’ says Martyn Bridges.

Call on an OFTEC registered installer to put in a new oil boiler. 

It’s worth getting three quotations when you’re buying a new boiler. Make sure they cover the same elements so that you’re comparing like for like. The installer will ensure the system is building regulations compliant and you should get documents to prove this. Keep these as you could be asked for them when you come to sell your home.

upgrade your boiler with Heatable

You can get your boiler replaced using an online provider like Heatable, which lets you change your system, move your boiler and introduce a smart thermostat

(Image credit: Heatable)

How much does a new boiler cost?

A straightforward gas boiler replacement plus thermostatic radiator valves will typically cost about £2,500, according to the Energy Saving Trust (EST). Replacing an oil boiler will cost about £3,200.

If you’re extending or renovating you may need to relocate the boiler, although, again, if it’s more than 10 years old replacing it should be considered. ‘If your boiler is basically brand new, you should expect to pay around £500 to £800 to move it to a new location,’ says Matthew Jenkins, heating expert at MyJobQuote. ‘This price will vary depending on the type of boiler you are moving, and you may have to pay extra to install new pipework. 

‘When relocating a boiler, it’s critical that you follow all applicable requirements and enlist the help of a Gas Safe Registered engineer,’ he adds.

How to take care of a boiler

For safety, boilers are designed to cut out if something is not quite right. An error code on the display will tell the engineer the cause of any problem.

A common reason for a boiler not operating is because the pressure in the system has dropped below the minimum level needed for it to work. Pressure loss is easy to resolve by topping up your system – check the boiler’s instructions to see how to do this, or ask your installer. However, it’s essential that the cause of the pressure loss is found – often this will simply be a tiny leak in the system or water supply problems in the local area.

Many problems are caused by something within the system (the pipes and radiators connected to the boiler) – usually air or dirt. Air can stop the water within the system from circulating properly, while dirt can foul parts in the boiler itself. If there are gurgling noises from radiators, or the top or bottom is cool, you’ll need to bleed the radiators. Remember to re-pressurise your system if you do this.

This may be a temporary fix, though, so your registered installer should investigate the cause. For this reason, manufacturers recommend that a central heating system is flushed before a new boiler is fitted, and that a filter is then fitted to protect the boiler from any dirt that might build up in the system over time.

An issue many combi boiler owners have experienced during harsh winters is due to frozen condensate pipes. If the pipe freezes, it will cause a boiler to shut down until the condensate melts. To prevent this, condensate pipes should be installed indoors, or adequately insulated.

A boiler should be serviced annually. This should pre-empt any problems and avoid a breakdown, as well as ensure the boiler is operating efficiently. If your boiler is still under guarantee, an annual service is usually part of the terms and conditions. It is illegal for an unqualified person to attempt to repair or install a boiler.

Tip: You may be insured for emergency boiler repairs under your home policy. However, policies may only be valid if the boiler has been serviced by a qualified person within the last 12 months, so make sure you check the details.

If you’ve taken out specialist boiler insurance you should be covered for emergency repairs and an annual service. These services generally cover repairs to the boiler, and some also cover boiler replacement, dependent on the model’s age.

What about boiler safety?

When fossil fuels, such as coal, wood, oil or gas don’t burn properly colourless, odourless carbon monoxide (CO) gas is formed, which is poisonous and can cause death. If the boiler isn’t working correctly, CO can be produced and therefore your Gas Safe or OFTEC registered engineer will check your boiler’s correct functioning and for CO during the annual service. It is also important to have an audible CO alarm in your home and to test it regularly. 

If your gas boiler has a flue that can’t be checked along its whole length, you should have inspection hatches fitted, so your installer can make sure there are no breaks in the flue that could leak carbon monoxide. If you prefer not to have hatches fitted, a boiler safety shutdown device can be installed. This features a detector that is fixed against the ceiling or wall that covers the flue, and has a sensor that goes through into the void, continuously monitoring for CO. If the poisonous gas is detected, it sends a signal to the boiler to switch off, and gives out a warning signal, so you know to call your Gas Safe-registered engineer.

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 Realhomes.com, 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.