What Boiler Do I Need With A Megaflo?

What boiler do I need with a Megaflo? This is a very common question that I get asked a lot but the problem I find is that most people don’t even know what an actual Megaflo is. So, before I answer this question, let me first begin by explaining what a Megaflo is.

What is a Megaflo?

A Megaflo is the award-winning product range from the manufacturer Heatrae Sadia. Is simply is a stainless-steel unvented cylinder which stores your hot water at mains pressure for your taps and showers. It allows for hot water to be available at all outlets and at mains pressure by being directly connected to the mains cold supply.

The way we commonly use the term ‘Megaflo’ is similar to how us Brits call a vacuum cleaner by the popular manufacturer’s name ‘Hoover’ instead of using its official term.

When it comes to electric heating and hot water products, Heatrae Sadia is top of the market. The Megaflo is one of their most popular ranges and for years it was one of the only unvented cylinders available and so it became common for people to call the system of an unvented cylinder, a Megaflo instead. This may cause some confusion when researching and possibly make it difficult to know what to look for if you’re looking at installing a Megaflo heating system. Just remember ‘Megaflo’ is not the official name for an unvented cylinder and it is just the name of a product range!

What boiler do I need with an Megaflo (unvented cylinder)?

Whether or not you have an actual Megaflo, with any unvented cylinder you will need a system boiler.

A system boiler directly heats your central heating system and produces hot water which is stored in the unvented cylinder. Once a hot tap gets turned on, hot water gets pushed out the tap by cold water which comes from the household’s main supply. This means you will not have cold-water storage tanks that could potentially take up space in your loft. Instead of this you will have high pressure hot and cold water, and this means you will have better performance for showers and baths. A system boiler works like a regular boiler in terms of they both need to store hot water. However, unlike a regular boiler, a system boiler sources water directly from your household’s mains.

A system boiler may be very useful if you have a large household with more than one bathroom. This is because the water pressure will not drop if more than one hot water outlet is opened at the same time. In this case a system boiler is more useful than a combi boiler system because in a combi boiler system, if more than one hot water outlets is opened then the water pressure is divided between the two and so the pressure drops. This can be annoying and difficult if more than one person is using a shower at the same time.

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Worcester Greenstar Range of System Boilers

Safety Precautions of an Unvented Megaflo System:

You have to be aware that any system has the potential to become faulty and so it is important to understand the safety measures that are put in place to reduce the risk of danger.

  • Installation – One of the most important safety measures of installing this system is that it must be installed by a fully qualified Gas Safe Registered plumber.
  • Pressure relief – If the pressure of the system is too high or the expansion of the system is faulty, there are expansion relief valves to ensure the pressure never becomes dangerously high.
  • Temperature relief- At the top of the tank there is a temperature/pressure relief valve so that water can be vented if it becomes too hot.
  • Regulating temperature – The ideal temperature of the water in the unvented cylinder is 60-65 degrees Celsius:

Unvented boiler systems require thermostatic controls, to ensure the temperature of the water in the unvented cylinder does not exceed 100 degrees Celsius. If the water temperature reaches 85 degrees Celsius the energy supply to the boiler is cut off, to prevent a further rise in temperature. However, in the case that the temperature reaches 100 degrees Celsius the temperature/pressure and expansion relief valves are used.

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Advantages and disadvantages of a system boiler:

Pros of installing a system boiler

  • Your household uses renewable energy – If your household uses renewable energy and your system boiler breaks down you will still have access to hot water. This is because the water stored in the unvented cylinder can be heated using an immersion heater or by the central heating system. This means it is compatible with any renewable energy sources you may use.
  • Easy installation – Many of the individual components of the heating and hot water system are built into the system boiler. This means it is much quicker and easier to install, compared to a regular boiler. The built-in components mean the unit is a lot more compact than a regular boiler and therefore only requires the unvented cylinder which can be stored in a cupboard.
  • Saving space – System boilers don’t require a cold-water feed tank or a feed and expansion tank as they can be used with pressurised cylinders. This could potentially save you quite a bit of space and it is ideal for households with limited space or no loft as there is no cold-water tank. Moreover, since the system does not need to be connected to a cold-water tank, you will be less restricted in terms of where to place it in your home.
  • Performance improvement – If you have a large household it may mean you have a high hot water demand. A system boiler allows the use of multiple taps simultaneously without a reduction in pressure, this is because it uses a large tank of stored water. This is ideal for busy households with more than one bathroom as it will improve the performance of your showers and maintain a consistent water pressure.
  • Stronger Water Pressure – Most other systems rely on gravity for their water pressure which can result in an inconsistency across your home depending on where the tap you are using is in relation to the system itself. In a system boiler, the water supply is delivered by the mains rather than a tank in the loft. This means there will be a consistent high pressure of water coming out of your taps compared to when you have a regular boiler.
  • More reliable – There are fewer components in a system boiler, this means it has a simpler plumbing system and is therefore easier to maintain and replace if it becomes faulty. Furthermore, this more simplistic system model also makes the system less likely to break down and become faulty, unlike other, more complicated systems.
  • Safety – The system boiler has multiple safety precautions and measures to limit danger and make sure the dangers of the system becoming faulty are minimised, overall reducing risk factors.

Cons of installing a system boiler

  • Hot water isn’t instant – The unvented cylinder can only hold so much hot water, this means it can potentially run out if lots of hot water is used. The system boiler will then have to go through the process of heating more water and filling the tank again before your home has hot water again. The amount of hot water you can use will be dictated by the size of your unvented cylinder.
  • They still take up space – System boilers will still take up some space in your home. Although they don’t need a cold-water tank, they still require the unvented cylinder. Even though a system boiler takes up less space than a regular boiler they still require a larger amount of space than a combi boiler.
  • The tank needs to be well insulated – To reduce the amount of heat lost and energy wastage, the unvented cylinder will need to be well insulated. Depending on where your unvented cylinder is installed, you may potentially need to invest in extra insulation for your unvented cylinder such as foamed polyurethane. You could end up spending more money than you initially planned to.
  • The dependence on the mains – If your mains system stops working, there is no backup store of water. The pressure of the hot water system will be limited to the pressure of the mains system so if your mains water supply has a weak pressure then the pressure of the hot water system will be equally as weak.
  • Extra costs – Your household pipework needs to be able to withstand the high pressures of the system. If you have weak pipework it could potentially mean you’ll have to replace them with better quality pipes which, as expected, is not a cheap process. As well as this, using an immersion heater to regulate the water temperature in your unvented cylinder will considerably raise the running costs. So, it’s advised to use this in emergencies only if the boiler breaks down.

How Much Does A System Boiler Cost?

There are many different system boilers available, these could range from around £500 to £3,500 without the cost of installation. Prices will vary, so doing research is vital.


Overall, if you have not yet invested into an unvented cylinder and system boiler then make sure you take the time to consider all the points made above. Installing a system boiler and an unvented cylinder may prove to be a lot costlier than you initially expected, however, it could prove to be well suited to your household.

If you have a large household then this system could be very convenient to you, especially if you have more than one bathroom as the performance improvement could be life changing. However, make sure you have the right conditions to invest into this system, for example being able to keep the cylinder insulated and having strong pipework otherwise you may find yourself spending more money than you thought.

Don’t forget there are plenty of other brands for an unvented cylinder if the Megaflo is out of your budget which are just as reliable!

A Heatrae Sadia Megaflo unvented stainless steel cylinder is one of the more expensive options. There are plenty of other manufacturers which supply unvented cylinders, so don’t feel the Megaflo is the only one out there because it’s the most common term you will hear. Just make sure to do enough research before investing into an unvented cylinder.

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MultiPlumb install Megaflo systems in South East London & Kent

Use this information as a guideline only but like I mentioned earlier, always consult an experienced, qualified Gas Safe Registered plumber to help you make the right decision for your home. It is not as simple as it sounds so leave it to us professionals!

Asking the right questions will mean that the plumber knows that you’ve done your research, so they won’t be able to misguide you in anyway. Make sure you have answered these before you come to a decision.

If you liked this blog post and found it useful I’d be grateful if you could help by sharing it with your friends and family on Twitter or Facebook.

If you have any questions feel to free to comment down below and I’ll answer them personally.

If you live in South East London or Kent and need some advice in terms of whether or not to install your boiler in your loft, then feel free to get in touch. We’d love to hear from you.

Richard Costello

Richard Costello, from Dartford in Kent, is the owner of MultiPlumb and has been involved in the plumbing industry installing bathrooms and boiler systems for over 15 years. If you have any questions or suggestions for future blog posts feel to get in touch at richard@multiplumb.co.uk.


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