Different Types of Boiler [Explained] – Combi, System, Conventional Boilers & More

Whether you’re trying to find a new boiler for your home or you’re simply wondering how different boiler types work, you’re in the right place. We’ve compiled our experience and resources to put together this handy guide to the different types of boiler systems.

After reading this guide, you’ll have all the behind-the-scenes knowledge you’ll ever need about the steamy, mysterious realm of boilers. Or, at the very least, you’ll be able to tell what type of boiler you’ve currently got in your house.

Different types of boiler

A Guide to the Different Types of Boiler Systems on the Market

There are 3 main boiler types out on the market today — combi boilers, system boilers, and regular boilers.

However, there are also outdated types, like back boilers, that still warrant a discussion because so many households still have them. And, there are overarching boiler categories, like condensing boilers, with which you should also be familiar.

Below, we’ll walk you through all of these different boiler types and categories.

Boiler Type: Back Boilers

We’re starting this guide with a boiler type that’s not popular at all: back boilers (yuck!).

Why is this boiler system a bust?

Because it’s inefficient, difficult to service, and possibly dangerous — especially if you don’t decommission it properly.

If you have a back boiler in your home, we’d advise switching and upgrading to a new central heating system, most likely one that incorporates a modern boiler type.

What Is a Back Boiler?

If you’ve purchased a new property, and can’t find the boiler, there’s a good chance it’s hidden in the fireplace; that’s a back boiler.

These types of boilers were introduced in the 1960s and were used in central heating systems until around the 1980s.

Needless to say, if you have a back boiler installed in your property, it’s going to be REALLY old. And with age, comes an incredible amount of heating inefficiency. Being ridiculously inefficient, it’s no coincidence that the big manufacturers no longer produce back boilers.

If you think you have this type of boiler, jump straight over to our guide to back boiler replacement here.

Or, you can get a Gas Safe heating engineer to help decide what the best route forward is with a free on-site visit and quote here.

Boiler Type: Combi Boilers

A combi — or a combination boiler — is by the far the most popular boiler type.

That’s because these boilers are most suited to small-to-average sized properties. We’re talking about a 1-bedroom flat, a 4-bedroomed detached house, and pretty-much everything in between that requires heat.

What Is a Combi Boiler?

Combination boilers are an extremely efficient way to heat your home and hot water as they require only a small amount of energy.

Combi boilers heat hot water on demand. So, as you turn up the thermostat, or turn on a tap or shower, the boiler heats water — just enough to meet your needs.

The great thing about this type of boiler? You won’t need any kind of water storage facility with a combi boiler.

And that’s going to save space in your home. After all, cylinders aren’t exactly small; they’ll take up the majority of space in an average airing cupboard.

The popularity of gas combi boilers has meant that most airing cupboards are now redundant. If there’s capped off pipework in your airing cupboard, it’s likely the central heating system has been upgraded from one of the boilers below; a system or conventional boiler. After it’s been upgraded, the cylinder would have been removed.

We’ve created a couple of guides for you to read on the topic, including one on combi boiler prices, and the best combi boilers currently available.

And, you can get an online boiler installation company like Heatable to offer you free expert advice with an online quote. All you have to do is fill in an anonymous questionnaire about your property, and you’ll get several boiler recommendations along with prices.

Worcester Bosch Greenstar 4000

Advantages of a Combi Boiler

  • Instant hot water and heating
  • Many boiler brands produce compact combis that can fit in a small kitchen cupboard
  • No need for a hot water cylinder, saving you space
  • Energy efficient, saving you up to £305 per year on your utility bills
  • No cold feed in the loft, meaning no risk of pipes freezing during winter
  • Cheap to replace in comparison to other types of boiler

Boiler Type: System Boilers

Whilst most homes either have a combi boiler, or upgrade to one, that doesn’t mean there isn’t a place for other boiler types, like system boilers.

What Is a System Boiler?

A system boiler doesn’t work like a combi; it doesn’t produce heating and hot water on demand. Instead, it fills up a cylinder.

Although there’s an obvious disadvantage to having to find space to install a hot water tank, there are some major advantages too.

In large properties with huge hot water demand, it comes to a point where it’s no longer viable to fit a combi boiler, and hot water storage becomes necessary to meet the increased demand. We’re talking about properties where multiple taps and/or showers are running at once.

You’re really going to struggle to get the heating output from a combi; sometimes, these boilers just can’t keep up with the need.

If you already have a system boiler with a hot water storage cylinder and use lots of hot water, you’re better off keeping your current setup.

Sound like the type of boiler you need? Check out our guide to system boilers, which covers everything you need to know about this type, including prices.

Advantages Of a System Boiler

  • No need for a cold water tank in your loft
  • Ability to provide large volumes of hot water for your home, via multiple taps and showers
  • Perfect boiler for properties with multiple bathrooms
  • Can be used with an existing cylinder (when in good condition), meaning boiler replacement costs are similar to combi installations (cheap!)

Boiler Type: Conventional Boilers

You’ll hear conventional boilers being called a few different things. That includes heat-only and traditional boilers.

What Is a Conventional Boiler?

Essentially, a heat-only boiler is an old-school version of a system boiler. But, instead of a simple water storage facility, it also needs tanks (usually located in your loft) to feed the boiler. Of course, the tanks take up extra space.

Most popular boiler manufacturers still produce heat-only boilers.

Whilst a system boiler might be a more viable option for your home, a straight swap for a conventional boile is the most cost-effective optionif you don’t plan to alter pipework in your central heating system.

But this isn’t a one-size-fits-all approach. Our suggestion would be to get a heating engineer to spec your property, consider what’s currently installed (in terms of the boiler and the pipework), consider your demand for hot water, and then help you decide on the right boiler. You can go and get a fixed-price boiler quote here.

If there’s no risk of a system or combi boiler putting current pipework under too much pressure, it’s likely one of these will be a better fit for your home than a conventional boiler.

We’ve created a guide to conventional boilers here.

Advantages of a Conventional Boiler

  • Ideal boiler for properties with low water pressure
  • Due to water storage facilities, it can provide high volumes of water to multiple taps and showers
  • Not essential to upgrade to a combi or system, so no need to replace your full heating system

Boiler Type: Condensing Boilers

Condensing boilers are boilers that can capture latent heat from escaping flue gases; this makes them more energy efficient than non-condensing boilers. All modern combis, system, and regular boilers are condensing boilers.

What Is a Condensing Boiler?

Due to new building regulations, boilers need to meet certain energy efficiency requirements. Non-condensing boilers don’t meet these requirements due to their inefficiency.

When a non-condensing boiler is firing, it wastes lots of energy via heat that’s expelled out of the flue. A condensing boiler recycles these gases and captures their heat. Essentially, it’s making use of energy that would otherwise disappear out of the flue.

We’ve already written a detailed guide to condensing boiler prices you can read here. Apart from flicking through this guide, you can also get free on-site boiler installation quotes from a qualified heating engineer here.

Home Installation Costs for Different Types of Boilers

Now you know which type of boiler you need, the next question is, how much will it cost to install?

We’ve created a range of guides to help you. Also have a look at our new boiler deals.

Boiler Installation Costs Depend On The Kind Of Boiler You Get For Your Home

If you own a back boiler, you’re most likely going to need to upgrade; check out our back boiler cost guide here.

For a typical gas boiler installation, including combi, system and conventional boilers, we’ve written a guide to boiler installation here.

But, if you’re off the grid, gas boilers aren’t an option. You probably use an oil boiler, and you can check out our guide to installing oil boilers here.

Finally, if you have no central heating in your property currently (you’re using storage heaters, for instance), we’ve also created a guide to the central heating installation.

Still Have Questions About Heating Boiler Types?

Still confused about the different boiler types and not sure which boiler is right for your home? You can ask a local Gas Safe boiler engineer for advice. They’d come over for a site visit, spec your property, and suggest a boiler type — and model — based on their findings. 

Alternatively, you can get a quicker answer by filling in Heatable’s online questionnaire. You’ll answer a few questions about your property and the current configuration of your heating system, and Heatable will suggest a range of suitable boiler models, along with fixed-price quotes.

Heatable boiler installations

FAQs About Types of Boiler Systems

Before we finish, there are a few common queries we’d like to address about different types of boilers.

What are the main types of boilers?

There are 3 main heating boiler types — combination boilers (aka combi boilers), system boilers, and heat-only boilers (aka regular, or conventional boilers).

Combi boilers rely on the mains water pressure to supply domestic hot water, which they produce on demand. They’re also capable of providing heating water to the home’s radiators and towel rails.

System boilers don’t heat water on demand; instead, they heat central heating water, which passes through a coil in a hot water cylinder, thus heating the water inside and getting it ready for the home’s taps and showers.

Conventional boilers work much like system boilers, except their water supply comes from a storage tank and a feed and expansion tank in the loft.

All 3 are commonly used in hot water and heating systems across the UK.

That said, combi tend to enjoy the most popularity, since there’s no additional equipment needed to operate them.

What type of boiler is best?

It depends on your hot water demands.

Combi boilers are the most popular, but that doesn’t mean that they’re the ideal boiler type for every household. They’re great for smaller households that don’t consume vast quantities of hot water simultaneously, i.e., no multiple showers running at the same time.

System boilers are ideal for thirsty households, particularly those that run multiple taps and showers simultaneously. However, they’re not ideal in small homes, where space is at a premium.

A heat-only boiler is also great for homes with high demand for hot water. However, such a boiler requires a hot water cylinder and water storage tanks; the latter should be located at the highest level of the house, typically the loft. If you don’t need extra storage space in your loft, a heat-only boiler may be a good option.

Note that your boiler options aren’t limited to combis, system, and regular boilers. There are also storage heaters, which are essentially electric radiator systems that accumulate heat during the night and give it off during the day. This type of heater makes sense if you’re on the Economy 7 tariff; otherwise, a boiler may be the better way to go.

Also, whilst natural gas may be the cheapest boiler fuel, it does have some drawbacks. Firstly, it’s not renewable, and its combustion emits CO2 into the atmosphere. What’s more, natural gas isn’t an option for households that live off the UK’s gas grid.

If you’re worried about your carbon footprint, and/or don’t have access to mains gas, you can consider an electric boiler or a biomass boiler as an alternative (be sure to read our guides to electric boilers and biomass boilers).

Which is the best gas boiler?

If you’re looking for a gas boiler, you can’t go wrong with installing a model from Worcester Bosch, Vaillant, Viessmann, Baxi, or Ideal. Each of these boiler manufacturers produce reliable, efficient boiler of different types (combi, system, and regular), and offer generous warranties.

Not sure which gas boiler will suit your property best? You can fill in this anonymous questionnaire from Heatable and explore your options.

What is a good boiler efficiency?

A boiler efficiency of 90% and up — A rating per the ErP ranking system — is the standard nowadays.  Most modern condensing boilers are designed to meet this standard.

However, if you’ve got an older boiler, particularly one that predates 2005, its efficiency may be far lower, and you may be overpaying on your heating bills.

For example, a boiler that’s over 20 years old may have an efficiency of only 60%, meaning you waste 40p for every pound you spend on gas. If you’ve got an old appliance, upgrading to a modern, condensing boiler will help you reduce your energy bills.

However, note that even the newest, efficient condensing boilers will not operate at their maximum efficiency if they’re not set up correctly.

Specifically, the boiler’s flow and return temperatures should be far lower than the level to which they’re normally preset. Instead of the customary 80C flow and 70C return, the temperatures should be set to 70C for flow and 50C for return — this will allow the boiler to use its “condensing” mode and capture latent heat from exhaust gases.

What are flue systems?

A boiler’s flue is a pipe that toxic allows exhaust fumes produced through combustion to be expelled outdoors. 

Boilers burn fuel — either gas, oil, or biomass — to generate heat and transfer it to central heating water and domestic hot water. The combustion process generates carbon dioxide, carbon monoxide, and water vapour; for safety reasons, these gases must be channeled away from the boiler and to the outdoors. A boiler flue acts as a fireplace chimney by directing these gases outside the building.

In most cases, a boiler flue will run horizontally to its exit location at the exterior wall. However, in some instances, the flue can also be vertical; this type of flue requires a cover to protect rainwater and debris from making their way inside.

Need More Help With Your Boiler?

Thanks for reading our guide to different boiler types; we hope the information here will help you in your search for a new boiler. You can check out more of our boiler guides here.

Is there anything we missed? If you have any more questions, please leave us a comment below and we’ll get back to you as soon as possible.



Avoid Expensive Breakdown Costs
Boiler Replacement Promise: If it's under 7 years old and we can’t repair it, we’ll replace it.
Try YourRepair. From £9/mo
All plans include: annual boiler service, all parts and labour, unlimited support and 24hr helpline.