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What is a Combi Boiler?

combi boiler diagram

Condensing combi boilers help save space, heating bills and the environment

Combi boilers just got better, the new generation of space saving boilers are highly efficient at their job which in turn reduces your carbon footprint. We take a closer look to see if they live up to the hype.

What is a Combination (Combi) Boiler?

Accounting for over half of new boiler installations high efficiency condensing combi boilers are a great space saving solution to that of a regular or system boiler.

Combi’s work by heating hot water on demand which removes the need for a hot water tank in the airing cupboard, this provides good efficiency in smaller properties as the water is only heated as and when required.

A conventional boiler will require a cold water tank in the loft, combi boilers take their feed direct from the mains supply which saves yet more space, no hot or cold water tank, as a result of this less pipework is required which generally results in lower installation costs.

A combi boiler also handles the central heating system, hence the name, Combination boiler. If you want to learn more about your heating system, check out our guide to central heating systems.

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When Should a Combi be Used?

It’s important to seek professional advice on which boiler is best suited to your requirements. For an idea of some of the top models on the market right now, see our guide to the best combi boilers in 2018.

In general a Combi boiler is a good choice if you live in a flat or wish to convert your loft into a living area.

If you have more than a couple of bathrooms or mains water pressure is low then a regular/conventional boiler is probably more suited, but remember, get professional advice.

A good reputable local plumber can be found at sites such as Boiler Guide or a nationwide company like British Gas Boilers can offer this for free.

Pros and Cons of a Combi


  • No tank or cylinder required
  • Minimal pipe work
  • Quick and easy installation
  • Mains pressure domestic hot water
  • Ideal for showers
  • Ideal for flats


  • Not good for multi bathroom properties
  • Require good water pressure
  • No airing cupboard or backup electric hot water heating (Immersion)


Are They Any Good?

As you can see in the table above the benefits far outweigh the disadvantages and will continue to do as long as the combi boiler continues to perform to a high level, at a reasonable cost.

This is the reason it’s installed in over 50% of domestic households. It doesn’t suit every household and if you do have space for tanks then a regular/conventional boiler may be more appropriate.

Please remember if you require a boiler service, repair or installation get professional advice, a good reputable local plumber or a nationwide company can offer this for free.

Combi Boiler Installers

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