Glass Lined Hot Water Storage Tanks

Glass Lined Hot Water Storage Tanks

Glass lined hot water storage tanks or glass-fused-to-steel tanks for storing hot water produced from water heaters such as tankless water heaters hot water system or indirect water heaters such as gas or oil boilers. From 200 to 6,000 Litres in volume by Flexiheat UK

Glass lined hot water storage tanks, also called vitreous enamel lined hot water tanks, are storage tanks or buffers that are normally used for domestic hot water storage(potable water), although the hot water doesn’t have to be of this quality. They are storage tanks manufactured in carbon steel but with glass or vitreous enamel corrosion protection of the metal surfaces in contact with the hot water.

The glass lining provides a robust internal surface for water storage tanks that must endure the wearing effects of high volume, high-temperature hot water and prevents corrosion of the storage tanks.

Glass Lined Storage Tanks

Our glass lined hot water storage tanks can also be used for cold water storage too, as they are designed to withstand temperatures down to 10 degrees C. The hot water temperature limit is 95 degrees C, depending on the model.

How is the vitreous enamelling or glass lining applied?

All interior linings of domestic hot cylinders must be “Food Grade quality” according to EU Regulation 1935/2004. Our vitreous enamelling has food grade certification at 95 °C, ensuring maximum quality at severe operating temperatures.

Using a sophisticated “surface treatment” on the carbon steel surface, combined with an automated enamel coating procedure, results in much more than a robust mechanical adhesion of the lining. A molecular interaction develops between the steel surface and the applied enamel layer during the curing process.

This maximum bonding of the enamel coating to the steel surface, along with the vitreous enamel’s high level of impermeability, makes the product last longer and keeps it from breaking down in ways that can happen with other types of coatings, like the protective coat coming off or blistering.

When to use glass lined storage tanks

These tanks are the most widely used for storing potable or waste water in building services or process equipment applications, but they are also suitable for dosing chemicals, numerous industrial effluents, or reagent materials since they combine the corrosion resistance of glass with the hardness of steel at a very cost-effective price.

Cathodic protection system via sacrificial anodes

A magnesium sacrificial anode in glass-lined tanks assures potable water quality. These sacrificial anodes guarantee that the domestic hot water is safe to drink by drawing contaminants from the nearby water supply. If the magnesium anode rods strike the glass while lying down, it might cause glass shattering or crazing (fine cracks on the surface of the material). It is critical that they be kept and carried upright.

The sacrificial anodes, through an electrochemical process, are designed to attract particles of limestone, iron, and other minerals present in the water and corrode instead of the glass lined tank. In simple terms, it “sacrifices” itself to help the range of glass lined storage tanks last longer.

Most glass lined storage tank manufacturers advise inspecting and evaluating the sacrificial anode’s condition every year and replacing it when it has been depleted by more than 50%. This is particularly important if you have hard water or use a water softener on your domestic hot water.

Storage Tanks Product Range

We have two ranges of glass lined water storage tanks; these are

Our SAC series

These have capacities ranging from 300 to 5,000 litres, with a maximum water temperature of 95 °C.

With a maximum working pressure of 10 bar for the 300 to 1,000 Litre capacity models

As standard, the 1,500 to 5,000 Litre tanks are 6 Bar rated – with the option of 8 bar manufactured units.

All units come with insulation with ErP energy ratings of “B” or “C” depending on size, to prevent heat loss.

Full details on this series of glass lined storage tanks are here –

Download the Flexiheat SAC Glass Lined storage tanks or cylinders for domestic hot water storage brochure

Finished in grey PVC RAL 9006 colour lining or jacket up to 2,000 litres, and white PVC RAL 9001 above this volume.

They are manufactured to the 2014/68/UE Directive, ART. 4.3, without CE marking Standard EN 12897:2016.
These buffers are designed and built in accordance with the requirements of 2009/125/EC.

Labelling in accordance with the requirements of 2017/1369/EU and Delegated Regulation 812/2013 (EU)

Glass lining corrosion protection to DIN 4753 and come with a 5-year warranty.

Our Coral Vito series

This series of glass lined water storage tanks has capacities ranging from 200 litres to 6,000 litres, with a standard pressure of 8 bar (10 bar optional upgrade) and a maximum operating temperature of 90 °C.

These hot water storage models all benefit from an inspection and clean outdoor or manhole which is 146mm for the 200 to 1,500 and a larger 400mm manhole option is available from 800 litres upwards.


800 to 1500 litre glass lined water storage tanks with large inspection plate or manhole 400mm -CV- RB range Flexiheat UK

RB models with larger 400mm inspection / clean out manhole


Full details are on the following brochure – please see page 10 for 200 to 1,500 Litre tanks , and pages 35 & 36 for the 1,500 to 6,00 Litre tanks

Domestic hot water cylinders and storage vitreous enamelled units from Flexiheat UK

Soft water areas: be aware

Glass-lined storage tanks can succumb to significant corrosive damage quickly under naturally soft water conditions, despite the use of sacrificial anodes.

Purer, soft water has poor electrical conductivity due to a lack of dissolved metal ions; therefore, the electrical flow from the anode to the cathode via the water is decreased. This has a negative influence on the chemical interaction between the sacrificial anode and the storage tank shell, resulting in less protection.

When the sacrificial anode is evaluated in such circumstances, its condition may be exceptionally good, but this is likely to be a significant signal that the anode is failing in its job, implying that the water tank itself is corroding.

An electrically powered anode is a common substitute for the sacrificial magnesium anode rods. A powered anode, which is frequently constructed of titanium, creates a very low current in the water rather than giving up its own electrons and creating an electrolytic current. This should provide a similar level of protection for a glass lined tank while not corroding the anode. However, in soft water conditions, even an electrically powered anode may still be ineffective since the conductivity required by the anode is insufficient.

As a result, in Scotland, west Wales, and the north-west and south-west of England, where the water is very soft, you are almost always going to need a stainless steel hot water storage tank.

Please see more on our range of stainless steel hot water storage tanks

Water heating

These glass lined storage tanks or buffer tanks are often used in conjunction with either tankless water heaters or suitable air source heat pumps, gas, or oil boilers that, via a plate heat exchanger, can provide the domestic hot water and space heating requirements. The glass lined storage tanks provide a buffer volume of hot water to accommodate a variety of peak demands the building or process may encounter.

Hot water system volume

With various capacities of tank sizes available, from a small 200 Litre to 6,000 litres in single tanks (you can also couple the units up in series should you require higher capacities), our range gives us the flexibility to cover all storage capacity requirements you may have.

Glass lined storage tanks

Should you require more product information, check stock, technical support, budget options, prices, or to place an order on our glass lined hot water storage tanks, then please don’t hesitate to contact our sales team on 01202 822221 or use our email contact form via the contact tab above to message us.