What Is a Megaflo Cylinder and Is It Worth Installing?

What Is a Megaflo Cylinder and Is It Worth Installing?

When people start looking for a new hot water cylinder, the name Megaflo normally appears fairly quickly.

Or Megaflow.

People spell it both ways, although the actual brand name is Megaflo.

It has become so well known that homeowners sometimes use “Megaflo” to describe any unvented cylinder, a bit like calling every vacuum cleaner a Hoover.

But Megaflo is a specific range made by Heatrae Sadia. It is not a different type of magical water storage invented by plumbing wizards.

So, is one right for your house?

Possibly.

They can provide excellent hot water pressure, faster filling baths and enough stored water for several bathrooms. But only when the cylinder is correctly sized, the incoming water supply is good enough and the installation around it has been designed properly.

Simply buying an expensive cylinder does not automatically improve a poor incoming mains supply.

Sadly, the shiny badge cannot alter physics.

Quick answer: What is a Megaflo cylinder?

A Megaflo is a branded unvented hot water cylinder made by Heatrae Sadia.

It stores hot water under mains pressure rather than relying on a cold water storage tank in the loft. This can provide stronger showers and faster filling baths, while removing the need for traditional gravity fed hot water pipework.

Megaflo cylinders are available in different sizes and configurations, including models heated by a boiler, electric immersion heaters or renewable technologies.

However, the performance depends heavily on:

• The incoming mains pressure
• The available water flow rate
• Correct cylinder sizing
• The heat source
• The pipework
• The controls
• The installation
• The number of outlets being used together

A Megaflo can be excellent.

An incorrectly sized Megaflo connected to a miserable water main is just an expensive cylinder having a disappointing day.

Is it Megaflo or Megaflow?

The official product name is Megaflo.

“Megaflow” is an extremely common spelling, and everybody still knows what you mean.

Megaflo is a range of unvented cylinders manufactured by Heatrae Sadia. The domestic Megaflo Eco range is promoted for high performance hot water, including powerful showers and faster filling baths.

What is an unvented hot water cylinder?

An unvented cylinder stores a large amount of hot water and is supplied directly from the cold water main.

Unlike a traditional vented cylinder, it does not normally rely on a cold water storage tank sitting in the loft.

That means the hot water can be delivered at, or close to, the pressure available from your incoming mains supply.

The cylinder is sealed and includes safety controls that manage pressure and temperature.

Typical components include:

ComponentWhat it doesPressure reducing valveControls the incoming water pressureExpansion provisionGives heated water somewhere to expandTemperature and pressure relief valveProtects the cylinder if temperature or pressure becomes excessiveExpansion relief valveReleases excessive pressureTundishProvides a visible indication of dischargeImmersion heaterProvides electric water heating or backupMotorised valveControls boiler heated water entering an indirect cylinder coilCylinder thermostatControls the stored hot water temperatureDischarge pipeworkCarries any safety discharge to a suitable location

Those parts are not optional decorations.

They are safety controls.

If one begins discharging, repeatedly dripping or behaving strangely, the answer is not to cap the pipe because the noise is annoying.

That pipe is telling you something.

Listen to it.

How does a Megaflo cylinder work?

Cold mains water enters the cylinder through a control set.

The water is then heated either:

• Through an internal coil connected to a boiler
• By electric immersion heaters
• Through equipment designed for a heat pump or renewable system
• Through a combination of heat sources, depending on the model

When you open a hot tap, stored hot water leaves the cylinder and fresh cold mains water enters to replace it.

Because the system is connected directly to the mains, it can deliver much better hot water performance than an old gravity fed cylinder.

But there is an important point here.

The cylinder cannot deliver more water than the property can supply.

If your incoming main provides ten litres per minute, fitting a cylinder capable of far more does not create extra water.

It is storage.

Not witchcraft.

What are the benefits of a Megaflo unvented cylinder?

Better hot water pressure

For many homeowners, this is the biggest reason to consider one.

A correctly designed unvented system can provide:

• More powerful showers
• Faster filling baths
• Better performance at taps
• Improved hot water delivery across larger homes
• The ability to use more than one outlet at a time

The final performance still depends on the incoming water supply and the pipework.

A proper survey should measure both pressure and flow.

Not look at the kitchen tap for three seconds and announce:

“Yeah, that seems alright.”

No cold water storage tank in the loft

A traditional vented hot water system often uses a cold water tank in the loft.

Removing that arrangement may:

• Free loft space
• Remove old storage tanks and redundant pipework
• Reduce the risk of contamination in an open tank
• Reduce the risk of a loft tank overflowing
• Simplify some plumbing arrangements

That does not automatically mean the entire installation becomes small.

The cylinder still needs space.

The valves need access.

The discharge pipe needs a proper route.

And somebody will need to service it later.

Stuffing it into a cupboard so tightly that the controls can only be reached by removing a wall is not clever use of space.

It is a gift to the next engineer.

Stored hot water for larger households

Combination boilers can provide excellent hot water in the right property.

But they heat water as it is used.

A stored hot water system gives you a reserve of heated water ready to go.

That can suit homes with:

• Several bathrooms
• Large baths
• High flow showers
• Multiple occupants
• Simultaneous hot water demand
• Larger hot water requirements

Correct sizing matters.

Too small and everyone runs out.

Too large and you are paying to heat and store more water than you realistically need.

Goldilocks had the right idea.

Not too big.

Not too small.

Just properly calculated.

Good heat retention

Modern cylinders use thick insulation to reduce heat loss while the water is being stored.

Heatrae Sadia’s Megaflo ranges are designed around high efficiency and heat retention, although the exact insulation, performance and specification depend on the particular model.

A well insulated cylinder still loses some heat.

All hot water storage does.

Anybody promising zero heat loss has either rewritten physics or misunderstood the brochure.

Different models for different systems

Megaflo cylinders are available in different sizes and configurations.

Depending on the property, options may include:

• Direct cylinders
• Indirect cylinders
• Solar compatible cylinders
• Heat pump compatible cylinders
• Higher capacity commercial cylinders
• Slimline models for restricted spaces

The domestic Megaflo Eco range uses an internal expansion arrangement on relevant models, while some larger Eco Plus products use a supplied external expansion vessel. In other words, do not assume every product carrying the Megaflo name is built in exactly the same way.

Direct or indirect Megaflo cylinder?

This is one of the first decisions.

Direct cylinder

A direct cylinder heats the water using electric immersion heaters.

It is commonly used where there is no boiler heating the cylinder.

This might suit:

• Flats without gas
• Properties using electric heating
• Certain off gas homes
• Installations where electrical hot water storage is required

Running costs need careful consideration because direct electric heating can be more expensive than heating water through a gas boiler or an efficient heat pump.

Indirect cylinder

An indirect cylinder is normally heated through a coil connected to a boiler.

The boiler heats primary water, which passes through the cylinder coil and transfers heat into the stored domestic hot water.

Most indirect cylinders also include an immersion heater for backup.

This is useful if the boiler fails.

Not enjoyable.

But useful.

Heat pump cylinder

Heat pumps often need cylinders with larger or specially designed heat exchanger coils.

A standard cylinder should not simply be assumed suitable.

The cylinder, coil, heat pump output and required reheat time all need matching properly.

“There’s a coil in it” is not a design calculation.

Is a Megaflo suitable for every home?

No.

It can be a brilliant product and still be the wrong product for a particular property.

Before recommending an unvented cylinder, we would want to understand:

• Incoming mains flow rate
• Incoming static and dynamic pressure
• Number of bathrooms
• Number of occupants
• Likely simultaneous water use
• Available cylinder space
• Discharge pipe route
• Boiler or heat source capacity
• Existing hot water pipe sizes
• Electrical supply for immersion heaters
• Water hardness
• Existing controls
• Whether the property has poor mains water supply

The incoming water supply matters

This is probably the most important part customers misunderstand.

An unvented cylinder uses the incoming cold main.

If that supply is poor, the hot water performance will also be poor.

Imagine pouring water through a drinking straw into a bucket and expecting a fire hose to come out the other side.

It won’t.

A proper assessment should check:

Static pressure

The pressure when no water is flowing.

Dynamic pressure

The pressure while water is being used.

Flow rate

How many litres of water the supply can deliver over a set time.

A property might show impressive static pressure, but the pressure collapses as soon as two outlets are opened.

That matters in a larger home.

Test it properly.

How large should the cylinder be?

Cylinder sizing depends on actual hot water use.

Things to consider include:

• Number of bedrooms
• Number of occupants
• Number of bathrooms
• Size of baths
• Type and flow rate of showers
• Whether showers and taps may be used together
• How quickly the heat source can reheat the cylinder
• Available space
• Future plans for the property

A small household with one bathroom does not need the same stored volume as a large family with three bathrooms and a bath apparently large enough to launch a canoe.

Bigger is not always better.

Correct is better.

Does a Megaflo give unlimited hot water?

No.

It stores a set amount of hot water.

Once that stored water is used, the cylinder needs time to recover.

The reheat time depends on:

• Cylinder size
• Stored temperature
• Boiler output
• Coil performance
• Heat pump output
• Incoming cold water temperature
• How quickly water is being used

A well designed system can recover quickly and provide excellent performance.

It is still not infinite.

If six people have back to back showers and somebody fills a large bath, the cylinder may eventually request a moment to itself.

Can several showers run together?

Potentially, yes.

That is one of the main attractions of an unvented cylinder.

However, successful simultaneous use depends on:

• Mains water flow
• Mains pressure
• Cylinder outlet capacity
• Pipe sizing
• Shower flow rates
• Cylinder volume
• Controls
• How much stored hot water remains

A brochure headline is not a promise that every house can run four rainfall showers at once.

The whole installation has to support it.

What is the difference between a Megaflo and a combination boiler?

Megaflo or unvented cylinderCombination boilerStores hot waterHeats hot water as it is usedNeeds cylinder spaceDoes not normally need a hot water cylinderCan suit larger simultaneous demandPerformance is limited by boiler output and mains supplyHot water can run out temporarilyDoes not run out of stored water, but has a maximum flow rateUsually has immersion backupNormally no electric hot water backupMore components and stored waterOften simpler for smaller homesCan work with boilers and other heat sourcesUsually uses the boiler itself for hot water

Neither option is automatically better.

A combination boiler can be perfect for a smaller home with one bathroom.

An unvented cylinder can be far better for a larger property with several bathrooms.

The right answer depends on the house.

Not which product the installer has sitting in the van.

Internal expansion or external expansion vessel?

When water heats, it expands.

That expanded water needs somewhere safe to go.

Some Megaflo models use an internal expansion arrangement. Other products and cylinder ranges use a separate external expansion vessel.

An internal expansion system can reduce the number of external components.

That does not mean it requires no maintenance.

The internal air volume may need to be recharged as part of servicing, following the manufacturer’s procedure.

If that expansion provision is lost, the safety valves may begin discharging.

We attend unvented cylinder faults where water is dripping through the tundish because the expansion provision has failed or lost its charge.

The dripping is the symptom.

Not the cause.

Changing the tundish will not fix it.

What is the tundish?

A tundish is the small fitting installed in the safety discharge pipework.

It creates a visible air gap so you can see if water is being discharged from a safety valve.

Under normal conditions, it should generally remain dry.

If water is passing through it, possible causes include:

• Lost expansion charge
• Failed expansion vessel
• Pressure reducing valve fault
• Expansion relief valve fault
• Temperature and pressure relief valve operation
• Excessive incoming pressure
• Debris affecting a safety valve
• Overheating

Do not ignore it.

Do not block it.

Do not fit a longer pipe so you can no longer see it.

The system is trying to give you information.

Does an unvented cylinder need servicing?

Yes.

An unvented cylinder contains safety controls that should be checked periodically.

A service may include:

• Inspecting the cylinder and visible pipework
• Checking the safety valves
• Checking the pressure reducing controls
• Checking expansion provision
• Inspecting the tundish
• Checking the discharge route
• Testing the thermostat and motorised valve
• Checking immersion heaters
• Inspecting for leaks and corrosion
• Confirming operating temperatures
• Checking the system against manufacturer requirements

The exact work depends on the model and system.

It should not be treated as a mysterious silver tank that nobody looks at until water starts coming through the ceiling.

Who can install a Megaflo cylinder?

An unvented hot water system must be installed by someone competent to carry out that work.

In England, an unvented hot water storage system above the relevant capacity is subject to Building Regulations. The installation must meet the hot water safety requirements in Approved Document G, including appropriate safety devices and discharge arrangements.

An installer may notify compliant work through an authorised competent person scheme, or the work may need to be dealt with through Building Control. Current government guidance lists authorised schemes covering heating and hot water systems, including unvented hot water storage.

People often refer to the required unvented qualification as G3.

Whatever label gets used, the important thing is that the person understands:

• Unvented safety controls
• Water Regulations
• Building Regulations
• Discharge pipework
• Temperature control
• Pressure control
• Commissioning
• Notification
• Servicing
• Emergency situations

This is not just a large kettle with some copper pipes attached.

Stored hot water under pressure needs treating properly.

Common installation mistakes

Not testing the incoming main

This is the big one.

A customer is promised amazing showers.

The cylinder is fitted.

The water main cannot supply it.

Everybody looks confused.

Test before quoting.

Fitting the wrong cylinder size

Too small and the hot water runs out.

Too large and the customer pays for unnecessary storage, equipment and heat loss.

Poor discharge pipework

The safety discharge must be routed and sized correctly.

It should not terminate somewhere unsafe, disappear into unsuitable pipework or be installed so badly that nobody can see a discharge.

Inaccessible controls

Valves and immersion heaters need access.

They will require servicing.

Building a beautiful cupboard around the cylinder and leaving a four inch gap is not craftsmanship.

It is sabotage with carpentry.

Poor pipe sizing

A high performance cylinder connected through badly sized pipework will not perform as expected.

The cylinder is only one part of the system.

Ignoring the boiler output

A large cylinder with an undersized heat source may take longer to reheat.

The stored volume, coil and boiler need to work together.

Failing to commission the system

After installation, the system should be filled, tested, commissioned and explained to the customer.

Not switched on while the installer runs towards the van.

Questions to ask before buying a Megaflo cylinder

Ask the installer:

1. What incoming pressure and flow rate have you measured?
2. What cylinder size are you recommending?
3. Why is that size suitable?
4. Is it direct, indirect or designed for a heat pump?
5. How long should it take to reheat?
6. Can my existing boiler heat it properly?
7. Will the existing hot water pipework need upgrading?
8. Where will the safety discharge terminate?
9. Is the cylinder accessible for future servicing?
10. What controls are included?
11. What paperwork and notification will I receive?
12. What maintenance will it need?
13. What happens if several outlets are used together?
14. What exactly is included in the quotation?

A competent installer should be able to explain those answers.

Not necessarily in painfully technical language.

But clearly.

Our professional recommendation

Do not buy a Megaflo simply because the name is well known.

Start with the result you want.

Do you need:

• Better shower pressure?
• Faster baths?
• More than one shower at a time?
• More stored hot water?
• Space freed in the loft?
• A system suitable for a larger family?
• A future heat pump compatible setup?

Then assess the property.

Measure the incoming main.

Calculate the hot water demand.

Check the boiler or heat source.

Inspect the pipework.

Work out where the cylinder and discharge can go.

Then choose the product.

A Megaflo can be an excellent option.

But it is the design and installation that create the result.

The logo on the cylinder cannot rescue bad pipework, poor pressure or someone making it up as they go along.

Megaflo and unvented cylinder installation across North Somerset

Kesselmann Heating & Plumbing installs, repairs and services unvented hot water cylinders across:

• Weston-super-Mare
• Clevedon
• Portishead
• Nailsea
• Bristol
• North Somerset and surrounding areas

We can assess:

• Incoming water pressure and flow
• Hot water demand
• Cylinder sizing
• Existing boiler capacity
• Pipework
• Controls
• Expansion arrangements
• Safety discharge routes
• Existing unvented cylinder faults

Then we explain the options.

Megaflo.

Another suitable cylinder.

A combination boiler.

Or keeping the system you already have.

We are interested in the correct result.

Not forcing the same shiny cylinder into every airing cupboard in North Somerset.