What is a Megaflow System?

Megaflo: What is a Megaflo Unvented Boiler System?

Megaflo: What is a Megaflo Unvented Boiler System?

More and more people are asking me about Megaflo heating systems, and if I would recommend them installing one into their home.

Before I can answer this question I first need to explain that Megaflo isn’t actually a heating system, it is simply the name of the product range by the manufacturer Heatrae Sadia. It is the heating system itself is known as an unvented boiler system.

A Megaflo is an award-winning stainless steel unvented cylinder which is designed to connect directly to mains cold supply so that hot water is available at all outlets and at mains pressure. It is similar to how us Brits call a vacuum cleaner by the popular manufacturer’s name ‘Hoover’ instead of using its official term.

Heatrae Sadia Megaflo

Heatrae Sadia Megaflo Stainless Steel Cylinder

Heatrae Sadia is the market leader when it comes to electric heating and hot water products and Megaflo is by far one of their most popular ranges. For years it was one of the only unvented cylinders available, as there wasn’t much competition, so it was common for people to call the system by the product name itself, instead of what it actually is. This can be confusing if you’re looking into installing a “Megaflo heating system” into your home, and it can be difficult to know what to look for when you’re doing your research.

Megaflo is the market leader in unvented stainless steel cylinders so it should come as no surprise that they are one of the most expensive options available. For households on a budget, a Megaflo may not be the best one to go for. In the UK there are plenty of other manufacturers which supply unvented cylinders, such as Worcester Bosch Greenstore, Telford Tempest or even an RM Cylinders Stelflow, all of which vary in price and quality, so don’t feel the Megaflo is the only one out there.

RM Cylinders StelFlow

RM Cylinders Stainless Steel StelFlow

So What Is An Unvented Boiler System?

To know whether or not you should opt for Megaflo, you first need to know what an unvented boiler system is. Essentially it uses an unvented cylinder to store pressurised hot water and once a hot tap is turned on, the hot water is pushed out of the tap by incoming cold water, which is sourced from the household’s mains supply. Because of this, there are no cold water storage tanks which need to be stored in the loft; no cisterns, expansion tanks or vent pipes, but instead high pressure hot and cold water, meaning improved performance for showers and baths.

The water stored in the cylinder can be heated using an immersion heater, or by the central heating system, making it compatible with solar thermal energy or any other renewable energy sources your household may use. This is also useful if the boiler breaks down as you will still have access to hot water.

The stainless steel cylinder often comes with a 25 year warranty thanks to the high quality, reliable metal it is made from, but the rest of the components usually only have a 1-2 year warranty. These features show the benefits of the unvented boiler systems, which is why they are becoming more and more popular in UK households. This also makes them different from vented systems which do need vent pipes and other separate units and components such as the expansion tank.

They are particularly useful in larger households with more than one bathroom as the water pressure does not drop if more then one hot water outlet is opened at the same time. In a combi boiler system if more then one hot water outlet is opened then the pressure is divided up between the two (not always equally) so the pressure drops. This makes it really difficult for more than one person having a shower./bath at the same time.

There are two main methods a system may use to accommodate water as it is heated. The first is an expansion vessel which uses the expansion of the water to compress trapped air, and increase the pressure of the water. The second is by trapping an internal air bubble in the cylinder (done by the plumber during installation). Similarly, the air in the bubble compresses as the water expands, increasing the pressure in the system. Both are highly effective but require certain safety measures to be in place in order to reduce the risk of possible danger if the system becomes faulty.

Dartford Golf Club Heating & Hot Water

Unvented Cylinders Installed at The Dartford Golf Club

Safety Precautions of an Unvented Megaflo System:

  • Unvented boiler systems use thermostatic controls, often ‘twin thermostats’, to make sure the temperature of the water in the unvented cylinder does not go above 100 degrees celsius:
    • The average or ideal temperature set by the controls are usually 60-65 degrees celsius.
    • If the temperature of the water reaches 85 degrees celsius the energy supply to the boiler is cut off, to prevent the temperature from rising.
    • If the temperature reaches 100 degrees celsius the temperature/pressure and expansion relief valves are used.
  • 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.
  • There is a temperature/pressure relief valve at the top of the tank, so that water can be vented if it becomes too hot.
  • 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.

Pros of an Unvented Megaflo System:

  • There is no cold water tank involved which has multiple benefits; firstly, there is no risk of the water being contaminated because of an open cold water tank, like with open vent boiler system. Secondly, it is ideal for households with limited space or no loft as there is no cold water tank to accommodate. Thirdly, since the system does not need to be connected to a cold water tank, you have more flexibility of where to place it (again, making it ideal for homes with limited spare storage room). Fourthly, because there is no cold water cistern which constantly need to be refilled, this system produces less noise in comparison to more complicated systems. And lastly, there is no risk of the system freezing up in winter, because there is no cold water tank to become frozen.
  • The system uses mains pressure. This means that the performance of showers and baths will improve, which is particularly ideal for homeowners who prefer ‘power showers’. It also means that the pressure of the water is consistent, no matter where you are in the house. Other systems make use of gravity for their water pressure, which therefore can differ depending on where the tap you are using is in comparison to the system itself. Thanks to the use of main pressure, this is never an issue with unvented boiler systems.
  • Since the pressure of the water is not affected by gravity, you can place the cylinder anywhere in the household, giving you more flexibility for where you store the cylinder.
  • Because there are fewer components involved and it is a simpler plumbing system, it is easier to maintain and replace if it becomes faulty. This also makes the system less likely to break down, compared to other, more complicated systems, so it is more reliable.
  • These systems are becoming more and more popular across the UK, so it is now relatively easy to get it repaired if it does break down.
  • The system can be heated using the central heating system or by heat immersion, making it solar thermal compatible, and if you already use a renewable energy source, the system can be connected to it, giving you the option to reduce your carbon footprint, if you so wish.
  • The system combines multiple safety precautions and measures to make sure the dangers of the system becoming faulty are minimised an ultimately avoided.

Cons of an Unvented Megaflo System:

  • There are some disadvantages involved with using the mains to supply the system. For example, there is no back-up store of water, if the mains system stops working for whatever reason. It also means that the pressure of the hot water system is limited to the pressure of the mains system. If your mains water supply has  particularly weak pressure, then the pressure of the system will be equally weak. Although there are ways around this so contact us if you’re not sure.
  • All household pipework needs to be able to withstand the high pressures of the system and if they don’t, you may have to have all pipework replaced with better quality pipes, which is not a cheap process.
  • Although it is not as noisy as some systems which use a water tank, the high velocity of the water flowing through pipes can create more noise.
  • The hot water cylinder can be seriously affected by heat loss, which is an inefficient use of energy. So depending on where the cylinder is installed you may need to invest in extra insulation for the cylinder such as foamed polyurethane, which will add to the installation costs.
  • Using an immersion heater will considerably raise the running costs, because electricity is three times more expensive than gas. So it’s best to use this in emergencies only if the boiler breaks down.

So, there you have it; a Megaflo unvented boiler system is not the only unvented boiler system out there, and now you know a bit more about how these systems work, as well as the pros and cons involved, you can decide whether they are the kind of system you need.

If the Megaflo brand doesn’t fit your budget, don’t forget that there are plenty of other brands to choose from, most of which are just as reliable. Although the unvented boiler system has its disadvantages, try to keep the advantages in mind as well, there are plenty of them. You can always ask your plumber if he thinks having this type of system installed is a worthwhile investment for you if you still are undecided.

MultiPlumb Dartford Kent

MultiPlumb are Fully Qualified Gas Safe Registered Plumbers

I would like to stress once again that it’s always important to get any gas related advice or installation work done from a fully qualified gas safe registered plumber. These types of systems can be very dangerous if they’re not installed properly so it’s worth checking the plumber’s reviews and qualifications.

If you live in South East London or Kent and need some advice in terms of what boiler system to choose for your home 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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