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Best hot water cylinders – unvented & open vent tanks

Best unvented hot water cylinder guide

System boilers and regular boilers can be used with hot water cylinders. They keep hot water from the boiler stored in a cylinder that can be used on hot water taps when they are needed.

These boilers are what people use when they say “Don’t use all of the hot water” in their homes. This is why the combi boiler is so popular as it does not require a hot water tank or a cold water storage tank.

Let’s look at how direct hot water cylinders work and the differences between them. After we’ve looked at each type of hot water tank, we’ll review the top ones on the market to be used with your heating system.

Unvented hot-water cylinder

These hot water tanks are mains-fed hot water cylinders. They have an inner coil but no open vent pipe. To allow heated water to expand, an expansion vessel is required.

Unvented hot water heaters are made from steel, not copper to withstand higher pressure. Unvented hot water tanks are fitted with safety devices that must all be installed and maintained only by licensed engineers.

A system boiler or regular boiler can also be used to install an unvented hot cylinder. This is a great option for homes with multiple bathrooms. This unvented hot water heater will reduce your heating costs, increase water pressure and meet your needs.

Installers who are professionals recommend unvented systems over traditional vented ones. To heat water, you can use an electric immersion heater with a hot-water cylinder.

If you are considering buying one of the best system boilers for your home, then why not upgrade your hot water cylinder if your old one is losing too much heat.

Advantages of unvented cylinders

  • These can supply hot water at high flow rates to multiple showers even if the mains pressure drops.
  • The unit can be placed in a way that allows for greater flexibility. They don’t need to be at the top of the system.
  • Rapid Recovery models allow for fast re-heat times.
  • Can be used in conjunction with solar panels

Disadvantages of unvented cylinders

  • These are more expensive to install than a new boiler.
  • To maintain them, they must be installed by an engineer who is qualified.
  • Other components have higher long-term maintenance costs

Open Vented hot water cylinder is another option

Open vent copper cylinders with are great when combined with a cold water storage tank. Open vent pipes extend from the copper hot water tank to the top and reach the top of cold storage tanks before connecting to them. The open vent pipe allows heat and excess pressure from hot water systems to escape in the event of an extreme heat fault.

They don’t rely on mains pressure to supply hot water at high flow rates. They can be retained even if the mains pressure drops. An unvented hot-water cylinder can be further improved by a pump. NB: Open-ventilated hot water systems are possible even if your heating system has been sealed.


  • They can supply hot water at high flow rates even when mains pressure is low.
  • Pumps can increase flow rates
  • It is possible to replace a copper unvented hot-water cylinder at an affordable price
  • Can be used in conjunction with solar panels


  • Copper tanks left uninsulated are inefficient.
  • The unvented hot water tank takes up much space
  • These should be at the highest point of central heating system

The best unvented hot-water cylinders right now

The best unvented hot water cylinder for you will depend on your home’s hot-water demand. There are many choices when it comes to choosing the best unvented hot-water cylinders.

These are the top unvented-cylinder manufacturers

  • Heatrae Sadia
  • Telford
  • Gledhill
  • Viessmann
  • Vaillant

Heatrae Sadia

Heatrae Sadia manufactures the Megaflo Eco Plus, which is one of the most widely-used unvented hot water cylinders on the market. These unvented hot water cylinders come with a lifetime warranty and a high flow rate. They are also very efficient in terms of heat retention and energy efficiency and come with built-in electric immersion heaters.

Over the years, Heatrae Sadia has earned a solid reputation. Megaflo Eco Plus is the best-unvented hot cylinder that you can purchase in 2023. Although these cylinders may be slightly more expensive than those mentioned, they are still a great hot water system in terms of value for money and will provide hot water without any problems.

Megaflo Eco Plus has a floating baffle expansion vessel within the unit. This ensures that there is no need for additional sections. These are the main features:

  • The capacity ranges between 250 and 1000 litres
  • High flow rates of up to 176 Liters Per Minute
  • Heating elements or heating coils are either electric or made of metal to quickly heat up.
  • An unvented hot water tank requires an external expansion vessel
  • SystemReady and SystemFit preplumbed options available for heat-only or system boilers
  • CFC/HCFC-free, 60mm injected foam offers heat retention and energy efficient.
  • The unique L-shaped immersion heater increases hot water volume

Megaflo Eco Plus Cylinders are covered by a lifetime warranty. They are undoubtedly the most reliable cylinders.


Vaillant is another well-known brand in the boiler market. UniSTOR hot water cylinders come with a 2-year labor warranty and a 25 year warranty on cylinder shells.

These units come in standard, slimline and pre-plumbed options. These units also feature improved insulation which reduces heat loss, makes them more economical and is energy-efficient. They can be attached directly to existing heating systems for ease of installation.

Vaillant uniSTOR unvented hot cylinders are available as a Slimline, Pre-Plumbed and Standard model. There are many features included in each model, including:

  • Standard cylinders 120l & 150l have an ErP–A-rating
  • Adjustable feet can be used to install on uneven surfaces
  • High insulation is used to reduce heat loss.

The cylinder shell comes with a 2-year parts warranty and a 25 year guarantee.


Some of the most amazing hot water cylinders in Telford are unvented. The Telford Tempest is the most well-known. This unvented cylinder is made from stainless steel and can be up to 40% thicker than other unvented models on the market.

Domestic Telford cylinders can store up to 500 litres water in direct or indirect cylinders. To meet your needs, you can choose between horizontal, slimline or pre-plumbed models.

The Telford Tempest Indirect Unvented Cylinder was designed for heating systems with a gas or oil boiler. These are the key features of the Telford Tempest Indirect Unvented Cylinders:

  • High resistance to corrosion is offered by Duplex stainless steel
  • The entire house is fully insulated to retain heat
  • A 3kW immersion heater
  • There are many capacities to choose from, ranging from 90 liters up to 500 litres

The components are covered by the 2 year warranty, and the inner container is covered by the lifetime warranty.


Gledhill’s Platinum Range is a new line of unvented cylinders that offers many unique features that are hard-to-beat. They are simple to install and come with an extended warranty of 25 years.

They are highly insulated to reduce heat loss, making them an industry leader in energy efficiency. They are smaller than the competition and can hold 300 litres for indirect cylinders, or 210 for hot water cylinders. Gledhill Platinum Range cylinders like the Telford Tempest, are made from tough and durable stainless.

Gledhill’s Stainless Lite Plus Indirect is a high-efficiency, unvented cylinder that can be used in a range of capacities to suit different property types.

The Stainless Lite Plus cylinder is the lightest on the market. High-efficiency corrugated tube coils have faster recovery times than regular tube coils. It has many other features, including a well-insulated shell to speed up heat recovery and a number of other benefits.

  • The water is heated efficiently and effectively by the corrugated coil.
  • Available in capacities from 90 L to 400 L
  • A 90-degree elbow and its light weight can reduce the time it takes to install.
  • To increase your energy efficiency, solar thermal and solar PV can be combined.
  • There are also slimline models to save space.

The warranty covers you for 25 years to ensure your complete protection


The Viessmann Vitocell 200V series of unvented, indirect heated cylinders can be used in conjunction with a Viessmann Vitodens Boiler. If an additional safety kit has been purchased, it can be used with non-Viessmann heating systems or traditional S and Y plan heating.

  • Capacity: Up to 300 Liters
  • Polyurethane foam insulation 50mm surpasses CHESS Best practice with energy losses as low at 1.4kW/24 hours
  • You can recover the heating coil in less than 19 minutes. This will allow you to heat water for 30 minutes.
  • A backup immersion heater (3 kW) is included.
  • Included with an expansion vessel external
  • Lightweight design makes it easier to install

Viessmann added a 25 year warranty against corrosion to the Vitocell 200V hot-water tank.

Which are the best unvented cylinders available in the UK?

Many new unvented cylinders are available on the market with new features and long warranties. We have four top-rated unvented cylinders that are guaranteed to last a lifetime.

Although the Gledhill Platinum Range is most striking, Heatrae Sadia’s reputation for quality will not let you down. Boiler Services can offer useful advice to help you select your next unvented cylinder.

You don’t want to hear the hot water tank roaring, so check out the top combi boilers available right now. These boilers are unvented and do not require external expansion units.

The best combi boilers are more efficient than system gas boilers in most cases because they don’t have to be on.

Our team of highly-trained installers will make sure that your product is installed efficiently and at a reasonable price.

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