​Boiler Types Explained: The Ultimate Guide

Thinking of buying a new boiler? Not sure the boiler you have is right for you? Know nothing about boilers at all?

For homeowners, understanding the differences between boiler types can be crucial to making sure you have the hot water and heating you need, when you need it. No one wants to be left with cold water and a cold house, so it’s important to ensure you have the right boiler for your home and that you’re taking care of your system.

The main things you should consider when looking at boilers is how much hot water your home needs and how much space you have. These factors will most directly affect your choice of boiler.

Boiler Types Guide:

Heat-only, combi, regular, closed-vent, open-vent – sifting through types of boiler can be confusing, but it’s not quite as complicated as it initially seems. Despite the variety of names, there are actually just three types of boiler that you’re likely to have in your home and they are: 

Combination boiler (AKA combi boiler)

Conventional boiler (AKA heat-only, open-vent or regular boiler)

System boiler (AKA sealed system or closed-vent boiler)

How do I know which type of boiler I have?

Combination boiler:

Your boiler will be a single unit, with no water cylinder or tank.

Conventional boiler:

Your boiler will have a boiler unit, a hot water cylinder, a cold water tank, and a feed and expansion tank (the tanks will likely be up in the loft).

System boiler:

Your boiler will have a boiler unit and a hot water cylinder (usually stored in an airing cupboard) but no water tanks.

What is a condensing boiler?

Condensing boilers aren’t really a type of boiler. The types listed above can all be condensing boilers – in fact, all modern boilers are. This means they can maximise the amount of heat you can get from your fuel and save you money on your heating bills.

Condensing boilers are more energy efficient because they are able to capture and reuse some of the heat that would escape from a non-condensing boiler’s flue.

If you’re concerned about energy-efficient boilers, all new boilers should be sold with an energy label (similar to those on white goods) so you can find out more information about your boiler.

How do different boilers work?

Now it’s time for the technical bit. Not interested? Skip ahead to find out which boiler type is right for you.

Combination boiler:

A combi boiler heats cold water taken directly from the mains when hot water or central heating is required, so there’s no need for large water tanks or cylinders. With all its parts hidden inside the boiler unit, it’s a compact system that manages heating water and central heating on demand.

Combi boilers have two heat exchangers - one for your central heating, and another for your hot water. Using a secondary heat exchanger makes combi boilers much more efficient than the coils used in hot water cylinders; this means they’re able to transfer heat as quickly as your tap’s running.

Conventional boiler:

A conventional boiler requires a large cold water tank to supply cold water from the mains and a feed and expansion tank that feeds the water into the boiler system and manages any water that expands after being heated.

The pressure in this system is gravity fed, so these tanks are usually fitted in a loft or attic because they need to be high above the boiler to increase the pressure of the water in your system.

When cold water feeds into your hot water cylinder, the coil inside the cylinder heats up the water around it which is then fed into your hot taps.

System boiler:

System boilers work in a similar way to conventional boilers, although they don’t require water tanks. This means cold water will be taken directly from the mains and fed into your hot water cylinder; the coil inside the cylinder heats up the water around it which is then fed into your hot taps.

Which is the right boiler type for me?

Combination boiler:

We’ll start off with the most popular boiler type in the UK – the combination boiler. These boilers are designed to provide heat and hot water, without the need for bulky water tanks and cylinders.

That means they’re ideal for people who have limited space or just want their boiler in a compact unit. You also get hot water and heat whenever you need or want it because combi boilers can heat water on demand.

One of the downsides of having a combi boiler is that your water pressure may be reduced if you run hot water from multiple taps at the same time (so no showers while someone’s washing the dishes).

As all the elements of a combi boiler are contained in such a small space, with all the moving parts inside the unit, there may be a greater potential for things to go wrong than with other types of boilers. But we’ll talk about ways to prevent that later!

Boiler cover quote

Conventional boiler:

Now let’s take a look at conventional boilers, which are also referred to as heat-only, open-vent or regular boilers. This type is the most traditional form of heating in the UK, though its popularity has largely decreased in favour of combi boilers in recent years.

With conventional boilers, the hot water stored in the water cylinder means that you can get hot water from multiple taps at the same time, so it’s ideal for larger households. You do need to have enough space to store the different elements, however, so they’re not ideal for homes where space is at a premium.

Conventional boilers also don’t give you hot water on demand. You can only use the amount of hot water that’s been stored in the cylinder, and once that’s gone you’ll have to wait for more water to heat up.

This type of boiler is great if you live in an older home in a low-pressure area too. The pressure you get will be gravity fed, rather than from the mains so it will be lower than other boilers that take cold water from the mains.

If you do need to get a new boiler and you already have an older system, they can often be more cost effective and less disruptive to replace, as you wouldn’t need to lay down more pipes and any older radiators would be more accustomed to the water pressure.

System boiler:

System boilers come with a water cylinder but no water tank that you’d have to fit into your loft (if you were interested in a loft conversion then this might be better for you than a conventional boiler).

They’re somewhat of a middle ground between combi and conventional boilers, as they’re more compact than conventional boilers, with higher pressure, and can provide hot water to multiple taps at once while retaining that pressure (where combi boilers can’t).

You will have to find a place to store the water cylinder (usually it sits in an airing cupboard, out of the way), so if you have a smaller home then this might not be the best option for you.

With system boilers, you don’t get hot water instantly and it can run out, meaning that you’ll have to wait for it to reheat.

If you have a system boiler, it’s recommended that you consider when you’re likely to need hot water and set a timer. Whether you have enough hot water or not will depend on the size of your hot water cylinder and how much you need.

Boiler quote cover

Do I need boiler cover?

No one wants to be without hot water and heating, particularly in the winter, so let’s look at what you can do to take care of your system. Try out a few of our boiler maintenance tips for some easy ways to look after your boiler.

Getting a boiler cover plan may also help to give you the assurance that you won’t be left floundering if your boiler suddenly breaks down when you need it most.

First off, if you’re renting a property then it’s the landlord’s responsibility to take out boiler cover, so you shouldn’t need to worry. If you’re a homeowner then take a look at your home insurance policy to see if your boiler is covered in your buildings and contents insurance.

Your boiler may also be covered with the manufacturer’s warranty (depending on how old it is), but it’s worth looking into what you’re actually covered for if you are going to rely on this to keep your boiler running.

Manufacturer warranties tend to cover faults and breakdowns for the boiler itself but not necessarily faults in the rest of your system.

Finding yourself with an issue and no boiler cover means you could end up paying an arm and a leg for a relatively small fix – and that’s not even thinking about the added stress of having to sort out an engineer to come and deal with your problem.

If you’re looking for the peace of mind that cover for your boiler can provide then you need to look into the types of cover available. Do you just want to cover your boiler? Do you want to add in heating cover? What about the plumbing and pipework?

At YourRepair, there are different levels of care available, from boiler care plans all the way to a complete home plan; plus every plan comes with an annual boiler service so you can relax knowing that your boiler has been checked.