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Hot Water Cylinders

When it comes to reliable hot water, few things work harder behind the scenes than your cylinder. Whether you're running the morning shower, filling the bath or powering the kitchen sink, your hot water cylinder keeps everything flowing smoothly.

At Thames Valley Plumbing Supplies, we provide a full range of hot water cylinders to suit all property types and heating systems. From traditional vented setups to modern unvented solutions, we stock trusted products for domestic and commercial needs alike. Whether you're refurbishing a single flat or managing a multi-storey build, getting the right cylinder is essential.

How Do Hot Water Cylinders Work?

Think of a hot water cylinder like a giant kettle or a thermal flask. It stores heated water and keeps it warm until you need it. Some cylinders heat water directly using an internal electric element, while others rely on an external boiler or renewable source like solar panels.

Once hot, the water sits inside the insulated tank, ready to be sent to your taps, showers or appliances on demand. The type of cylinder you need depends on your heating system, water pressure and the size of your property.

Before you dive into choosing a cylinder, it's worth understanding the different types available and how they work. From vented to unvented, direct to indirect, each has its own strengths depending on your setup. Let's take a closer look.

Types of Cylinders

Hot water cylinders come in several varieties, each designed to suit different systems and needs. Understanding the key differences will help you choose the right cylinder for your property and hot water demands.

Vented vs Unvented Cylinders

Vented Cylinders

How They Work
Vented cylinders are part of a traditional gravity-fed system. Cold water is stored in a tank in the loft, which feeds the cylinder using gravity. The water is then heated and stored in the cylinder, ready for use around the home.
Advantages
  • Simple system with fewer parts
  • Usually cheaper to buy and maintain
  • Compatible with older plumbing setups
  • Doesn't rely on high mains pressure
Disadvantages
  • Lower water pressure at taps and showers
  • Needs space in the loft for a cold water tank
  • Less efficient than modern alternatives
Best For
Vented cylinders are ideal for older homes that already have a gravity-fed system in place. They're also a good option where mains pressure is low or unreliable.

Unvented Cylinders

How They Work
Unvented cylinders are fed directly from the mains water supply. Because the system is sealed and pressurised, water comes out at a much higher pressure. Heating can be supplied via a boiler or an internal immersion heater.
Advantages
  • High water pressure for better showers and faster baths
  • No need for a cold water tank in the loft
  • Space-saving and neater installation
  • Hygienic, sealed system
Disadvantages
  • Higher upfront cost
  • Must be installed by a qualified G3-certified engineer
  • More components, so a bit more can go wrong
Best For
Unvented cylinders are ideal for modern homes with good mains pressure, especially where multiple bathrooms or high water demand is a factor.

Direct vs Indirect Cylinders

Direct Cylinders

How They Work
Direct cylinders heat water using an internal electric immersion heater. There's no boiler involved, so they operate as a standalone unit.
Advantages
  • Simple to install and operate
  • Doesn't rely on an external boiler
  • Good for properties without gas
  • Can be used as a backup system
Disadvantages
  • Typically more expensive to run (especially on standard electricity tariffs)
  • Slower to reheat compared to boiler-fed systems
Best For
Direct cylinders are a good fit for smaller properties or flats without a central heating boiler. They're also handy for backup hot water in case the boiler fails.

Indirect Cylinders

How They Work
Indirect cylinders rely on an external heat source, usually a gas or oil boiler. A coil inside the cylinder carries hot water from the boiler, which heats the surrounding stored water without mixing.
Advantages
  • Generally more energy-efficient
  • Heats water faster when paired with a boiler
  • Can still include an electric immersion heater for backup
Disadvantages
  • Requires a compatible boiler
  • Slightly more complex to install
Best For
Indirect cylinders are the standard choice for homes with a central heating boiler. They're reliable, efficient and can handle high hot water demand with ease.

Solar Cylinders

How They Work
Solar cylinders are a type of indirect cylinder designed to work with solar thermal panels. They usually feature two coils: one connected to the solar panels and the other connected to a boiler for backup heating.
Advantages
  • Uses free energy from the sun, reducing energy bills
  • Environmentally friendly
  • Works alongside your existing boiler
Disadvantages
  • Higher upfront cost for the cylinder and solar system
  • Needs a suitable roof for solar panels
  • Performance depends on sunlight and weather
Best For
Solar cylinders are ideal for eco-conscious homeowners looking to cut long-term heating costs. They work best when combined with other heating systems and when the property gets good sunlight.

Brands We Stock

We supply hot water cylinders from some of the industry's most trusted names. Known for their build quality, reliability and long-term performance, these brands are used by professional installers across the UK in everything from new builds to renovations.

Gledhill LogoOso Hotwater LogoUK Cylinders LogoMegaflo LogoTelford Logo

Compliance and Safety

Unvented hot water cylinders are classed as pressurised systems, which means they come with specific safety requirements under UK law. By regulation, they must be installed and signed off by a qualified professional with G3 certification.

This is not just a box-ticking exercise. These systems hold hot water under pressure, so correct installation is essential to keep everything safe and running as it should. The right safety valves, expansion controls and discharge pipework all need to be in place and properly set up.

If you are working on a project involving an unvented cylinder, make sure the installer is fully certified. It protects the property, the people in it and keeps everything within the current building regulations.