What types of boiler are there, and which is best for me?

Confused about combi boilers, system boilers and conventional boilers? Here’s everything you need to know about the differences between the three main domestic boiler types.

The three types of boiler you need to know about

Trying to find the right type of boiler for your home can be overwhelming. With so many different options available on the market, it’s hard to know where to start, let alone how to figure out the best home boiler system for you.

But it needn’t be daunting. There are basically three main domestic boiler types to choose from. We’ll walk you through the types of boiler available and help you to work out which is the best type of boiler for your home and family.

Combination boilers

What is a combination boiler?

A combi (short for combination) boiler is the most compact option because it generates both your heating and hot water from a single unit, usually wall hung. With a combi boiler, there’s no need for a separate hot water tank.

How do combination boilers work?

Combi boilers are connected to the mains cold water supply and can heat water on demand. They burn fuel when you ask for hot water and have an integral heat exchanger that then gets hot enough to instantaneously heat the cold water from the mains supply as it flows over it.



Space saving – no need for a separate water tank

Pressure problems – functionality depends on mains
pressure, so they won’t work as well if you have poor flow rates
or incoming water pressure

Neater looking – everything is hidden away in one unit

Solo use – the flow rate drops if you want hot water in more
than one place, so they’re not a great idea if you have more
than one bathroom and people often shower at the same time

Easily serviced – they’re so popular, most engineers are
trained to work on combi boilers so it’s easier to find someone
to help if something goes wrong

Limited choice – power showers aren’t an option with a combi
boiler because they rely on a hot and cold water feed from a
gravity-fed system

Instant heating – you get hot water when you want it without
waiting for a tank to heat up

Moving parts – because the boiler unit has moving parts,
there is more potential for things to go wrong

Cheaper maintenance – generally the integral heating and
hot water functions are covered by the manufacturer’s warranty

Solar incompatibility – most, but not all, combi boilers aren’t
compatible with solar water heating systems

Energy efficient – new models boast over 90% efficiency

Money saving – energy efficiency also means lower bills

Easy installation – there’s just one unit to fit, and no extra
water tanks to worry about

Safer water – you get water straight from the mains, so it’s
safer and fresher than if it had been stored in a tank

Is a combination boiler right for me?

A combi boiler is the right type of boiler for you if you have:

  • A small household
  • Only one bathroom
  • No loft to put a hot water tank in
  • 10 radiators or fewer

Conventional boilers

What is a conventional boiler?

Also known as a ‘regular’ or ‘heat-only’ boiler, conventional boilers are one of the types of boiler that has a water tank. They heat up your radiators directly and connect to a separate cylinder or tank to provide hot water.

How do conventional boilers work?

As with combi boilers, a heat exchanger warms water when fuel is ignited, but with a conventional boiler a pump transports the water to a storage tank. This hot water then flows through to radiators to heat them, or into your taps when you switch them on.



Multiple use – hot water can run from several taps at once

Water wait – hot water isn’t always available on demand, you
need to allow time for the cylinder to heat up

Solar compatible – to lower your bills and do your bit for the

Less efficient – conventional boilers aren’t as efficient as
combi boilers because heat is lost from the water stored in the

Back up – even if your boiler breaks down, you can still have
hot water if an electrical immersion heater is installed in the

Pricey installation – can be more expensive to install if you
don’t already have cold water and expansion tanks

Money saving – these are the cheapest boilers to replace

Bulky system – you’ll need space for the tanks as well as the

Low pressure – conventional boilers don’t rely on high mains
pressure, so are a good option for older heating systems

Limited water – once the hot water tank runs out, you’ll have
to wait for it to refill before you can have any more hot water

Is a conventional boiler right for me?

A conventional boiler is the right type of boiler for you if you have:

  • A larger household
  • More than one bathroom
  • Low mains pressure
  • An older house

System boilers

What is a system boiler?

Like conventional boilers, system boilers need a hot water cylinder. However, unlike conventional boilers, they don’t need a cold water tank, and components like pumps and valves that are separate in conventional boilers are built-in with a system boiler. You might also hear system boilers being called ‘closed vent’ or ‘system sealed’ boilers.

How do system boilers work?

System boilers work in the same way as conventional boilers, it’s just the components are slightly different. Think of them as the modern upgrade to a conventional boiler.



Space saving – as many of the components are integrated,
and it doesn’t need a cold water tank, system boilers don’t take
up as much room as a conventional boiler

Pressure problems – as with combi boilers functionality
depends on mains pressure, so they won’t work as well if you
have poor flow rates or incoming water pressure

Less worry – there are no components in the attic, so you
don’t need to fret about potential leaks or freezing in the winter

Quicker install – there are fewer pieces to fit, so it can be
installed quicker than a conventional boiler

Is a system boiler right for me?

A system boiler is the right type of boiler for you if a conventional boiler is suitable and you:

  • Don’t have low mains pressure
  • Have a relatively modern central heating system

Thinking of updating your boiler?

Now you know more about the different types of boilers, but you can still learn more to become a boiler guru. Check out our guide on improving your boiler’s efficiency to find out how to get your existing system back on track. And learn more about boiler specs (no, not a boiler that wears glasses), but useful information that will help you when picking a new boiler.

Thinking of updating your boiler? Get started by answering a few questions and we’ll help you to find your perfect boiler.