Heatrae Sadia and Megaflo cylinders and water heaters

A Megaflo is an unvented hot water cylinder, not a boiler. It stores hot water and delivers it directly from the mains water supply, with no separate cold water storage tank in the loft¹. The brand has been part of Heatrae Sadia since 1993, and Heatrae Sadia describes it as the market leader in the unvented hot water cylinder sector, to the point where Megaflo is seen as the generic term for unvented water heating².

For a household, that means mains-pressure hot water at every outlet simultaneously, and no dependence on a tank in the roof for supply. What it does not change is the fuel: an indirect Megaflo is heated by a System or Heat Only boiler, so the home stays on gas or oil and on a supplier, and a direct cylinder runs on electricity from the grid³. The cylinder itself is a store, and storage is the part of a hot water system a household can control.

What a Megaflo cylinder is: unvented storage, not a boiler

An unvented hot water cylinder stores hot water and delivers it directly from the mains water supply, with no separate cold water storage tank¹. That is the whole distinction from the vented cylinders that preceded it, and it is why the Megaflo name carries weight: Heatrae Sadia states that its Megaflo unvented cylinders were the first hot water cylinders to feature an integral floating baffle, which takes up the expansion as water is heated¹⁰.

The contrast with a combi is worth stating plainly. Combi boilers do not use a hot water cylinder at all, because all the heat and hot water comes directly from the boiler itself⁵. A Megaflo does the opposite: it separates the heat source from the store, which is what allows a cylinder to be fed by a boiler, a heat pump, an immersion element or a solar arrangement without changing the cylinder.

The Megaflo Eco range uses a high performance coil-in-coil heat exchanger, which transfers heat from the sealed primary coil for the central heating system to the coil for water heating¹⁰. Megaflo unvented cylinders have been providing hot water solutions to UK homes for over 30 years¹¹. The first Megaflo unvented cylinder came from Hotflo in 1987, and Heatrae Sadia acquired the brand in 1993².

Megaflo and Heatrae Sadia: who makes them and where

Heatrae Sadia designs, engineers and manufactures in the UK¹². The Megaflo Compact SystemFit is described as proudly made in the UK from the highest quality duplex stainless steel, and the Megaflo Commercial Flexistor is designed, engineered and manufactured in the UK⁷. The Hotflo unvented water heater is also manufactured in the UK¹³.

The brand history runs in steps. The first Megaflo unvented cylinder came from Hotflo in 1987, Heatrae Sadia acquired Megaflo in 1993, and the Megaflo Commercial product line was introduced in 2011². In 2012 the brand marked its 25th anniversary and the Megaflo Eco Plus model was introduced². Megaflo Commercial and Megaflo Eco Plus unvented calorifiers are manufactured on the company's XL production line, because the larger capacities and pressures require different manufacturing techniques from the domestic unvented cylinders¹⁰.

Heatrae Sadia's wider product range covers hand dryers, water chillers, immersion heaters and unvented cylinders, and the company states that its range is stocked by all the leading merchants¹⁴. For a household, UK design and manufacture shortens the parts and service chain, though it does not change the fact that the cylinder is a component in a system whose fuel comes from elsewhere. The ownership structure behind the brand is covered in Is Heatrae Sadia part of BDR Thermea?, and the wider cylinder market in Hot Water Cylinder Manufacturers in the UK.

Direct or indirect: how each model heats your water

The two families differ only in where the heat comes from. On an indirect unvented cylinder, hot water from the boiler, heat pump or solar thermal system circulates through a coil inside the cylinder, transferring heat without the two water supplies mixing¹. On a direct cylinder, the water is heated by an immersion heater within the cylinder itself.

The Megaflo Eco Indirect cylinder is compatible with System or Heat Only boilers³. The Megaflo Eco SystemFit cylinder comes equipped with factory-fitted plumbing and wiring, making it ready for use with a heat only boiler, and the Megaflo Compact SystemFit is likewise ready for installation with a heat only boiler³. The Megaflo Eco range is sold as both direct and indirect cylinders¹⁵.

The older vented cylinder market used the same direct and indirect split: the most common vented cylinders are the direct, heated by immersion, or the indirect, heated by a boiler utilising an internal coil¹⁶. What changed with unvented cylinders is the supply pressure, not the heating logic.

For a household, the choice is a fuel choice. An indirect cylinder keeps the home on whatever heats the primary circuit, which in most UK homes is gas. A direct cylinder runs on electricity, which means the grid and a supplier, but it also means the cylinder can be heated from a solar PV diverter or a cheap overnight tariff without any boiler involvement. The Megaflo Eco Solar PV Ready is an unvented cylinder that heats water by harnessing surplus solar electricity, and it is available in direct and indirect forms¹¹.

Sizes and specifications: 70 to 2,500 litres

The domestic range covers the usual household sizes and the commercial range goes far beyond it. The Megaflo Commercial Flexistor offers 400 to 2,500 litre capacities to suit most installation requirements⁶. The Megaflo Compact SystemFit 2sf holds 180 litres⁷.

The commercial range also offers a wide choice of auxiliary elements including combinations from 6 to 54kW⁶. For comparison, a vented cylinder datasheet in the same market lists a 570 mm cylinder diameter across 120, 140, 180 and 210 litre models, with a 1670 mm height on the 400 litre model and 1870 mm on the 250 and 300 litre models¹⁷.

Two temperature rules bear on any stored water cylinder. UK building regulations advise that water cylinders need to regularly reach temperatures of more than 60 degrees C⁹. Independent guidance is firmer still: where a boiler has a hot water cylinder that stores water for later use, a minimum water temperature of 60 degrees C is needed to kill Legionella bacteria, and flow temperature should not be adjusted beneath 65 degrees C without consulting an engineer first because of the Legionella risk¹⁸. A cylinder thermostat should not be allowed to drop below its set point, because that can cause bacteria to grow in the tank²⁰.

Materials and design: duplex stainless steel and the floating baffle

The cylinder body is the part that has to last. The Megaflo Compact SystemFit is made in the UK from the highest quality duplex stainless steel, and the Megaflo Commercial Flexistor is manufactured from duplex stainless steel⁷. The Megaflo Eco Solar is constructed from Duplex stainless steel cylinder material²¹. The same material choice appears across the wider market: STEELflow unvented cylinders are manufactured from premium grade duplex stainless steel¹⁶.

The design feature that distinguishes Megaflo is the expansion arrangement. Heatrae Sadia states that its Megaflo unvented cylinders were the first hot water cylinders to feature an innovative integral floating baffle, which takes up the expansion as water is heated¹⁰. The Megaflo range uses this internal floating baffle expansion system⁴. That is what removes the need for an external expansion vessel on the domestic models, and it is the component behind the air gap regeneration procedure described in the FAQ.

The Megaflo Eco range uses a high performance coil-in-coil heat exchanger, which transfers heat from the sealed primary coil for the central heating system to the coil for water heating¹⁰. A faster coil means the cylinder recovers more quickly after draw-off, which matters more in a household with several bathrooms than the headline capacity does.

Cost: £500 to £1,500 plus VAT and installation

There is no single published Megaflo list price. Two figures circulate for the cylinder alone, and they disagree: £500 to £1,500 and £1,000 to £3,500. The documents do not resolve which applies, so both should be treated as indicative rather than as a quote.

What is published is a comparison figure for a different product class. Independent statistics list a wall-mounted electric boiler with cylinder at £1,750 to £2,000, an average of £1,875²². That is a complete electric heating and hot water package, not a cylinder, and it is included here only because it is the nearest published figure in the same market.

In practice a Megaflo is bought as part of an installed job. Heatrae Sadia's guidance is that a qualified installer will be able to purchase the cylinder from a trade merchant, and that homeowners interested in buying a Megaflo product should use the Megaflo Find an Installer tool¹⁴. That route produces an installer-quoted price covering the cylinder, the controls, the pipework changes and the notification work, and it is the figure a household should work from.

VAT treatment is not stated in any of the figures above, so they should be read as quoted rather than as confirmed VAT-inclusive prices. The Megaflo Main range is exclusive to independent merchants, which affects where a quote can be sourced but not the installation rules¹⁵.

Warranty: 25 years on the cylinder, with conditions

The cylinder body carries a long warranty and the components do not. All unvented cylinders are provided with a 25 year manufacturer's warranty on the cylinder body against material defects and manufacturing faults, with 2 years on all components¹⁶. The Megaflo Compact SystemFit is backed by a 25 year warranty⁷. Heatrae Sadia describes its Megaflo cylinders and calorifiers as having an industry-leading lifetime warranty in domestic installations, and the Megaflo cylinder warranty as transferable¹⁰.

Registration runs through the Heatrae Sadia online form, and the company asks that Heatrae Sadia or Megaflo product warranties be registered within 30 days of installation⁵. The split between a 25 year body warranty and a 2 year component warranty is the practical point: the steel is covered for decades, the immersion element, thermostat and valves are not. The general rules on keeping a registration valid are set out in Registering a Warranty and Keeping It Valid.

Installing a Megaflo: the unvented qualification and flow rate test

Unvented work is regulated work. Installers of unvented cylinders must carry a qualification to install them, and the work is notifiable under Building Regulations¹⁰. That is not a manufacturer preference; it is a condition of the product type, and it applies to every unvented cylinder regardless of brand.

The buying route follows from that. A qualified installer will be able to purchase the cylinder from a trade merchant, and homeowners interested in buying a Megaflo product should use the Megaflo Find an Installer tool, which finds a local qualified installer¹⁴. Heatrae Sadia's product range is stocked by all the leading merchants¹⁴.

The SystemFit and SystemReady variants reduce site work by arriving with factory-fitted plumbing and wiring. The Megaflo Eco SystemFit cylinder comes equipped with factory-fitted plumbing and wiring, making it ready for use with a heat only boiler, and the Megaflo Eco SystemReady cylinder is designed for easy on-site installation with a system boiler on the same basis³. The Megaflo Compact SystemFit adds factory-fitted plumbing and wiring⁷.

A mains flow rate and pressure check is the other half of the assessment, because an unvented cylinder delivers whatever the incoming mains can supply. Where the incoming supply is weak, the cylinder will underperform regardless of its capacity. The installer qualification requirement is common across the market and is covered in Manufacturer Installer Networks and Accredited Schemes.

Where a Megaflo falls short: mains dependence and siting limits

The dependence is the mains. An unvented cylinder stores hot water and delivers it directly from the mains water supply, with no separate cold water storage tank¹. That removes the loft tank and the header pressure limit, and it replaces them with a hard dependence on the incoming mains: pressure, flow rate and continuity of supply all come from outside the home, and a mains interruption stops hot water at the tap.

Siting is the second limit. A cylinder needs a floor-standing position with the height and width to match the model, and the commercial sizes run to 2273 x 304 mm on the 1450 litre model and 2035 x 1470 mm on the 2000 litre model⁶. The Megaflo Eco Slimline Direct is a compact version of the Megaflo Eco cylinder, which addresses footprint rather than capacity¹¹.

The fuel dependence remains whatever the cylinder does. An indirect Megaflo is compatible with System or Heat Only boilers, so the home stays on gas or oil and on a supplier³. A direct cylinder runs on electricity from the grid. The Megaflo Eco Solar PV Ready reduces that dependence by using surplus solar electricity to generate hot water, but it does so only when the sun is generating and the surplus exists¹¹.

Buying and owning: merchants, installers and UK support

The purchase route is installer-led. A qualified installer will be able to purchase the cylinder from a trade merchant, and homeowners interested in buying a Megaflo product should use the Megaflo Find an Installer tool¹⁴. The Megaflo Main range is exclusive to independent merchants¹⁵. Heatrae Sadia's product range is stocked by all the leading merchants¹⁴.

Support is UK based. Heatrae Sadia's customer support team provides the aftersales service, and a visit can be arranged on +44 (0)344 871 1535, with genuine parts orders and enquiries on option 5 of the same number⁸. The supported services cover specification, sales, genuine parts and aftersales support, and the helpline handles ordering information, service or repair booking and warranty registration⁵.

Documentation is centralised. Heatrae Sadia maintains a literature library of brochures, installation guides and user guides, available to view and download from one centralised location, including an archive for discontinued products¹². Superseded models are listed with their replacements: Megaflo HE maps to Megaflo Eco, Megatech Solar maps to Megaflo Eco Solar, and PremierPlus maps to the Megaflo Eco SystemFit cylinder²³.

On the renewables side, the Megaflo Eco SolaReady package comprises an unvented hot water cylinder, a factory wired and plumbed pump station, and a selection of collector arrangements to suit a variety of requirements²¹. The Megaflo Eco Solar PV Ready is an unvented cylinder that heats water by harnessing surplus solar electricity, in both direct and indirect forms¹¹. Both keep the cylinder as the store and change only what fills it.