What are the different boiler types, and which boiler do I need?

What are the different boiler types, and which boiler do I need?

Posted on May 17, 2021

Maybe you’re in the market for a new boiler, or perhaps you would like to know whether the type of boiler you already have is the right choice for your home.

In this quick guide to boiler types, we’ll explain the different types of boiler as well as the pros and cons of each one so you can decide which is the best boiler for you.

What are the different types of boiler?

You get three main types of boiler:

  • Combi boiler – These produce instant hot water
  • Heat only boiler – Also known as conventional or regular boilers, these work with a hot water tank or cylinder in the loft
  • System boiler – You’ll mostly find these in more modern homes, with an ‘unvented’ hot water cylinder on the first floor

Let’s take a closer look at each one, and help you identify whether you have the right boiler for your home.


The Combi Boiler

What is a combi boiler?

A combi boiler has no hot water tanks and generates all the heating and hot water for your home from one single unit.

How does a combi boiler work?

A combi boiler provides instant hot water by heating water directly from the mains using an integral heat exchanger inside the boiler.

A combi boiler doesn’t need hot water tanks or cylinders as everything is done through the one unit. Because there are no tanks, no hot water is stored like in conventional boilers, and all water is heated when needed.

Combi Boiler – The Pros

  • If you are replacing a system or regular boiler with a Combi boiler, then you will be creating space by removing the old hot water cylinders /boiler, tanks
  • The integral heating and hot water functions are covered by warranties and guarantees from boiler manufacturers, so help with low maintenance costs
  • You don’t have to wait a long time to get hot water

Combi Boiler – The Cons

  • If you have a property with poor water pressure coming in, then combi boilers don’t work as well
  • If you need to provide hot water to two outlets simultaneously, for example a property with multiple showers, then the hot water rates are reduced
  • It’s a common mistake to end up with an oversized combi boiler for homes with 15mm pipework. If you have a combi boiler that can provide 12.5 litres of hot water per minute (or more) then it won’t be as effective in homes using 15mm pipework. You can read more about the problems an oversized boiler can cause here.

What is a heat only (conventional / regular) boiler?

It’s pretty much what it says on the tin. If you have a heat only boiler, then it will only provide heating, and will be accompanied by a hot water cylinder.

How does a heat only boiler work?

With a conventional or regular, heat only boiler, you provide heating directly to the radiators. The hot water cylinder provides the hot water.  You will often find this type of boiler works with a Feed and Expansion tank located in the loft, called an ‘open-vented’ heating system. A heat only boiler will also work on a sealed system as well, using a hot water cylinder in an airing cupboard.

If your home has a heat only boiler located in a chimney breast with a fire in front, it’s unfortunately not possible to replace it in the same location. This type of heat only boiler is called a back boiler and would need to be replaced with a heat only boiler somewhere else in the home, or perhaps a combi boiler.

A Heat Only Boiler – The Pros

  • If your home has older radiators, then heat only boilers tend to work well with them. System or combi boilers can cause leaks in older radiators which are put under the higher water pressure
  • Heat only boilers are the cheapest you can buy, so have low replacement costs

A Heat Only Boiler – The Cons

  • A heat only boiler has many other parts within the whole heating system (hot water tank, pumps, valves). Unfortunately, these aren’t covered by manufacturer guarantees or warranties, which could prove costly when they breakdown and need repairs


What is a system boiler?

A system boiler works with a steel hot water cylinder for hot water production, but has all the same other components as a combi boiler.

How does a system boiler work?

System boilers are like a more modern version of the heat only (regular / conventional) boilers. Like heat only boilers, system boilers use a hot water cylinder. The main difference is that system boilers don’t use an open-vented system. This means that components like valves and pumps are integrated inside the unit rather than linked to a tank in the loft. They are often installed with unvented hot water cylinders.

System Boiler – The Pros

  • If your property has multiple showers, then the system boiler is great as it can provide for high hot water demand simultaneously to multiple outlets
  • As most of the systems components are inside the boiler unit itself, you get good cover from manufacturer warranties and guarantees
  • System boilers rely on good incoming water pressure from the mains. The internal flow rates depend on this, so if the water pressure coming in is poor, the internal pressure will be poor as well
  • If you are replacing a combi boiler with a system boiler, you will need more space in order to home the hot water cylinder. These are usually placed on the first floor, in an airing cupboard or similar
  • A heat only boiler (open vented system) is a better choice than a system boiler if you have pipework under screed, or old radiators, in order to avoid leaks and deliver appropriate water pressure


Hopefully you will now be able to identify what type of boiler you have in your home, and whether you need to consider a replacement.

Our expert heating engineers work locally across the South Coast, from Hampshire to Berkshire, Surrey and South London, and Wiltshire to Sussex. If you’re not sure your boiler and heating system are working efficiently or you’ve been experiencing problems, get in touch with us today. You can also get a quick, easy quote for a new boiler on our website here.