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Combi boiler vs system boiler – Which is best?

If you’re considering replacing or upgrading your boiler, we examine combi boilers vs system boilers to help you choose what’s right for you.

Boilers are a must-have appliance in any home, but they are an investment. If you’re considering replacing or upgrading your boiler, we recommend you read this article where we carefully examine combi boilers vs system boilers to help you choose what’s right for you and your home.

What is the difference between a combi boiler vs a system boiler?

Combi boilers are more modern and provide hot water and heating immediately on-demand, as soon as you turn on a tap. System boilers use a cylinder to store hot water, as there is no hot water heat exchanger to keep a constant supply. When you turn on the taps, your hot water will be drawn from this supply tank.

Pros & cons of a system boiler


  • Easy to install.
  • Stronger water pressure.
  • Quick response to demand.
  • Solar thermal compatibility.


  • Take up more space.
  • Insulation.
  • Limited by tank size.

system boiler tankSystem boilers are particularly popular in homes that have a higher than average demand for hot water. They are a good choice if you are replacing an old boiler, as a system boiler will be more energy efficient. If you have solar panels, you might be pleased to know that some system boilers are compatible with solar thermal energy, meaning you could also save money.

System boilers are also known for providing a good hot water flow rate, as the water supply is taken directly from the mains.

Having a hot water tank is helpful if you have multiple people running a bath simultaneously; the downside is that your home needs to be able to accommodate the size of this water tank. This tank also needs to be surrounded by insulation to keep the water warm, which takes up even more space. This is one of the main drawbacks of a system boiler vs a combi.

Pros & cons of a combi boiler


  • Energy-efficient.
  • Compact.
  • Quick and simple installation.
  • Instant hot water.


  • Can’t meet high hot water demand.
  • Weak mains pressure.
  • It might not be compatible with older pipework.

Combi boilers vs system boilers are much more economical on space. Combi boilers are more compact and usually fit into a kitchen cupboard, and there is no need for a tank. No tank means instant access to hot water – no waiting for the tank to refill!

Combi boilers are also more energy-efficient which could mean a reduction in your energy bills. If you’re environmentally conscious, you’ll be pleased to know that all new combi boiler installations are required to meet an energy efficiency rating of 92%.

So far, so good for combi boilers vs system boilers. However, you can run into difficulty if you want to install a combi boiler into an older property. Combi boilers operate at a higher pressure, so you need to make sure your existing pipework can cope.

If you live on a new build development, you may find that water pressure is a challenge for a combi boiler if the flow rate to your home is weak due to smaller pipework.

Which is best? Combi boiler vs system boiler?

system boiler water tankNeither is better or worse, as it depends on your home and your requirements. Before making your choice, think about the demands on the system and what infrastructure and space you have at home.

A bigger family home with multiple bathrooms might make a system boiler a better choice. However, if you are a single-person household or a couple, a combi boiler would be a great choice.

Deciding between a combi boiler vs a system boiler is an important decision. If cost is an important factor in your decision making, then take a look at our boiler cost guide. You can also review previous water bills to see how much water you are consuming.

If you are unsure about the suitability of your pipework or space in your home for either type of boiler, then contact a recommended local heating engineer who will be more than happy to advise you.

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Is a combi boiler cheaper to run?

There are many points to consider when choosing a new boiler, and the cost is just one of them. Potentially a combi boiler may be cheaper to run, but the real deciding factor is your water consumption. A combi boiler is more energy-efficient, but if you are using a lot of hot water consistently, it may not be as cost-effective.

Is a system boiler better than a combi?

It really depends on your individual circumstances. Think about your water usage requirements and space considerations in your home. Ultimately, if you are unsure, consult with a heating engineer who will be best placed to advise you on your individual requirements.

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