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Advanced Knowledge Centre

Mega Flow or Combi – What’s best?

How to choose between Mega Flow or Combi

If you’re choosing a new boiler, the you may be confused with the vast choice. Do you go for Mega flow or a Combi boiler? This article explains the difference between Mega Flow and Combi (Combination) boilers and what they are best for. Thus, comparing the two options so you can make an informed choice.


How many bathrooms will be used at the same time?


If you are likely to have more than 1 bathroom in use at once, such as a large family home with more than 3 bathrooms, then you’ll need a an unvented hot water storage vessel, such as a Mega Flow, which is the manufacturer’s name for an unvented hot water vessel.


Mega Flow


Mega Flows come in all different sizes. You can connect Mega Flows to solar panels or the electric supply.


A Mega Flow can also connect with a gas boiler. It’s connected straight to the incoming water mains, so you get a high pressure supply of hot water.


Combi Boiler


Combination boilers (also known as combi boilers), on the other hand, provide instant hot water without the need for any hot water tank, which means you save on space as you don’t need any cupboard to store the hot water vessel. In addition, they are very efficient to run.


Mega Flow – Pros:Mega Flow Unvented Water storage vessel


  • Lots of stored hot water
  • High pressure and volume of hot water up to 25 litres a minute
  • Can run up to 3 baths at the same time
  • No need for booster pumps for showers and baths
  • No need for cold water storage tanks as all off the mains water
  • Can use solar panels to heat water to reduce fuel costs
  • Can be installed when there is no gas supply to property
  • Electrical heat back up if boiler breaks down


Mega Flow – Cons:


  • Will take up storage space
  • Very heavy and bulky
  • More electrical and mechanical controls to breakdown
  • Takes about 45 minutes to recover when all the stored hot water is used up
  • Less energy efficient to run than a combination boiler if connected to electric only
  • You need a minimum flow rate of 16 litres of water from your water main with a minimum of 1 bar operating pressure on a 22mm diameter cold water main pipe
  • Large sized water supply
  • More maintenance as the unvented storage vessel and the boiler will have to be serviced every year
  • You need to heat the whole storage vessel even if you only use a basin of hot water


Combi Boiler – Pros

combi boiler

  • Takes up very little space
  • Doesn’t need much water pressure to operate only 0.7 bar. Or 7 litres a minute
  • Instant hot water when you need it only 20 seconds heat up time
  • You can have as little or as much as you wish of hot water as you like
  • Very energy efficient as there’s no need to heat any storage vessel
  • Half the cost of an unvented cylinder and boiler installation
  • Cheaper to maintain and service
  • Therefore, perfect for smaller properties (3 bedroom and under)
  • No risk of legionella
  • Can run on oil, gas, electric and LPG
  • Fast installation
  • Less electrical and mechanical controls to breakdown


Combi Boiler – Cons


  • Can only run 1 bath at a time
  • Will not cope with more than 2 bathrooms working at one time
  • May require bigger gas supply
  • Needs gas to property
  • Can only deliver a maximum of 16 litres a minute of hot water
  • Not suitable for large properties with more than 2 bathrooms


Mega Flow or Combi – Which is Right For You?


So which is right for you? Mega Flow or Combi? As you will have seen, it largely depends on the number of bathrooms you have. If your property is 3 bed or under, then consider the Combi boiler. If you have more than 3 bedrooms and more than 1 bathroom plus you have the storage space, then a Mega Flow will be a good option.


What next


If you need more help choosing or want us to install your Mega Flow or Combi boiler, then contact us.


Book your appointment by contacting us today.

Disclaimer: The information contained on this website if for general information purposes only. You should not rely upon the material or information on the website as a basis for making any decisions or actions and we don’t accept liability for anything you chose to do with the information.