This website uses cookies to ensure you get the best experience on our website. Find out more.

What is a Combi Boiler

Combi boilers are the most popular type of boiler system in the UK, suitable for a range of different homes and needs.

A combi (or combination) boiler is a type of boiler system that can provide both heating and hot water all through one single compact unit. Unlike heat-only and system boilers, combi boilers do not require an additional hot water cylinder or cold water tank for water storage – they get their water directly from the main supply.

How Do Combi Boilers Work?

When you need hot water for your taps or radiators, cold water from your main supply is fed directly into the combi boiler.

They are seen as very cost-effective as water is heated on demand rather than stored in a separate cylinder. The hot water is delivered at main pressure to ensure you get a powerful shower without the need for a separate pump.

This heated water is sent to your radiators and taps when needed via the diverter valve.

Modern combi boilers are manufactured with condensing technology. This means they recycle energy by extracting latent heat from flue gases which would have otherwise been wasted. They are thus regarded as an efficient form of heating.

Pros and Cons of Combi Boilers

To help you get a better understanding of combi boilers, below we provide a breakdown of their main pros and cons.


  • Instant hot water– As water is supplied and heated directly from the mains instead of being stored, a combi boiler can deliver hot water to your taps and radiators on-demand.
  • Compact in size– Combi boilers’ compact size and ability to work without storage tanks and cylinders make them a great choice for homes with limited space. A combi boiler can fit into a standard-sized kitchen cupboard.
  • Energy-efficient –Modern combi boilers, with their condensing technology, are designed to provide effective heating whilst using minimal energy. This helps to reduce the impact on the environment.
  • Savings –When used efficiently, a combi boiler can help you save up to 35% on your energy bills.
  • Longevity– When maintained properly and serviced regularly, a combi boiler is estimated to last up to 15 years in operation.


  • Not a suitable choice for large homes– Although combi boilers can deliver both hot water and heating, they cannot do so at the same time. They also cannot provide hot water for more than one bath or shower simultaneously. This makes them potentially unsuitable for larger homes with high hot water demands.
  • Reliance on mains pressure– Due to hot water being supplied directly from the mains, you must have good water pressure in your area in order to get the best out of your combi boiler. Substandard main pressure can hinder the performance of your combi heating system.
  • Cannot be paired with a power shower– Combi systems are not compatible with boiler pumps, plus they do not feature the storage cylinder that power showers require.
  • No Immersion heater –Combi boilers don’t need a water tank, so you won’t be able to have a backup immersion heater in case of a system breakdown.

How Much Does A Combi Boiler Cost?

On average, a combi boiler can cost between £1,200 – £3000 including installation. The total cost of the combi boiler installation will depend on the brand, model and size of the boiler being fitted, as well as the cost of the parts and labour required for the installation.

Are Combi Boilers More Energy Efficient?

Yes, combi boilers are regarded as more efficient than heat only boilers. Although both boiler types are condensing, the fact that combi systems do not store their hot water makes them more efficient. The water stored in the cylinder of a heat-only boiler system can cool down over time. When this happens, the heat only system will have to use energy to heat the water back up. This does not occur with combi boiler systems as the water is fed directly from the mains, thus the system only uses energy to heat the water that you need.

Looking for boiler cover for your combi boiler? Get in touch with our expert team today to find a suitable boiler cover deal for your home.

Get a new boiler