It's time for an update

You've been using your good friend IE for quite some time now. It has been a reliable companion for probably the last 20 years.

Unfortunately, due to technology constantly evolving, we would like to kindly ask you to update your browser to one of your liking from the ones listed below. This will ensure that you're going to have good time on our site. Actually, any site really.

Farewell, Internet Explorer.

What is a hot water cylinder?

hot water cylinder with a golf club and gold balls on a table

What you'll learn

  • How do hot water cylinders work?
  • What is the difference between a direct and indirect hot water cylinder?
  • What are the advantages of a hot water cylinder?
  • How long does a hot water cylinder usually last?
  • How do I know if my hot water cylinder needs replacing?

Many households rely on hot water cylinders for their central heating and hot water, but few know exactly how they work or how to diagnose potential issues until it’s too late. Below is our comprehensive guide to hot water cylinders.

What is a Hot Water Cylinder?

A hot water cylinder is a well-insulated tank which stores water after it’s been heated. Water is heated through your boiler system and is then stored, at temperature, ready for you to use whenever it’s needed. By storing hot water in this way, there’s no need to run the heating system constantly resulting in lower energy bills, without subjecting household members to cold showers.

Do I Need a Hot Water Cylinder?

If you have a system or open vent boiler, heat pump, or solar hot water solutions then you will need a hot water cylinder installed as part of your heating and hot water system.

If you own a home with two plus bathrooms and a high demand for a constant supply of hot water, then installing a heating system which utilises a storage cylinder will ensure your needs are always met. For properties where low pressure is an issue and a pump is needed to support the flow of water to the shower, a hot water cylinder will ensure that water is delivered at the right temperature.

Our range of hot water cylinders are designed to work in perfect harmony with our range of domestic heating solutions. Browse the range below to learn more or talk to a member of our team today for advice about what size or type of cylinder you require, or any other questions you might have.

Ready to choose? Find an accredited Vaillant installer near you today.

How do hot water cylinders work?

Many households rely on hot water cylinders for their central heating and hot water, but few know exactly how they work or how to diagnose potential issues until it’s too late. Below is our comprehensive guide to hot water cylinders.

A hot water cylinder is a tank used for storing hot water for later use. There are two main types of hot water cylinders available in the UK;

  • Pressurised unvented hot water cylinders
  • Vented hot water cylinders

Unvented hot water cylinders receive water directly from the mains, therefore benefiting from the greater levels of pressure than a gravity-based system and distributing water more easily throughout the home. This is a benefit to its design and a reason behind its growing popularity since it was first introduced to the UK in the 1980s.

Unvented hot water cylinders do not require a separate cold water tank. This makes them more compact than other systems that need additional space in attics and lofts.

A vented hot water cylinder receives its water from an external cold water tank (also known as a header tank) often stored in the attic of a home. This system is usually found in the attic because it uses gravity to build pressure rather than pressure generated from the mains. It is called a vented hot water cylinder because a vent pipe is used to connect the hot water cylinder to the header tank.

Watch our video on 'What is an unvented hot water cylinder?'

What is the difference between a direct and indirect hot water cylinder?

As well as choosing between an unvented or vented hot water cylinder, there is the consideration over whether it should be directly or indirectly heated.

Direct

A direct hot water cylinder heats water through an immersion heater found inside the cylinder. The cylinder is therefore not connected to a boiler.

Indirect

An indirect hot water cylinder heats the water using an external heat source such as a boiler. The water is heated in the cylinder through a coil that is heated by the appliance.

What are the advantages of a hot water cylinder?

  • Suitable for larger homes

    Hot water cylinders are a great choice for larger homes with greater demands for hot water. While combi boilers are able to heat water on demand in smaller properties, they cannot cope with several taps, showers and radiators being turned on simultaneously. Boiler systems that use hot water cylinders, however, can store large quantities of hot water in advance. This hot water can then be sent throughout the home as needed.
  • Versatile

    A hot water cylinder is also a versatile option for modern homes. Water can be heated either directly or indirectly or through sustainable means like solar power and biomass fuels.
  • Backup hot water

    A vented hot water system backup heat source can also be added to an indirect boiler system to ensure that hot water is available should the boiler fail.

Points to bear in mind

Less efficient

Most hot water cylinders are heated in advance, and more than necessary which could result in higher energy and water bills. However, these can be combined with smart controls or built in to a hybrid system in order to better utilise energy.

Limited hot water supply

Another disadvantage is that a hot water cylinder can only hold so much water before it runs out. The hot water cylinder is typically sized to the requirements of the general household demand to give enough hot water on a given day. However excess use may result in having to wait for the cylinder to refill.

Less pressure

Vented hot water cylinders use gravity to build pressure for the water, which means that certain parts of the home do not receive equal levels of pressure. Upper floor bathrooms, for example, may experience lower levels of water pressure than kitchens on the ground floor.

More complex to install

Due to the water being stored at a higher pressure in unvented hot water cylinders, the system requires additional safety features which can increase the cost in comparison to a vented hot water tank.

Having a bubble top unit - a unit with an internal air bubble that is trapped in the cylinder upon instalment.
Installing an external expansion vessel

How do I know if my hot water cylinder needs replacing?

Hot water cylinders are usually reliable but can experience irreparable problems over time. The signs you can look out for are:

  • Cold water

    If your home has a direct hot water cylinder , cold water could be a sign of an issue with the internal heating element. This element wears down over time and may need replacing by a qualified Gas Safe Registered (GSR) engineer. However, if your hot water cylinder is nearing 8-12 years it is advisable to have the whole boiler looked at by a GSR engineer to see whether the entire system needs to be changed.
  • Leakages

    If you spot a leak in your hot water cylinder it is recommended that you arrange for a GSR engineer to inspect your system as soon as possible. Not only can leaks be dangerous, they also signal that there is an internal issue that cannot be repaired.
  • Strange noises

    Limescale builds up in cylinders over time and causes blockages. If your system is not regularly maintained you may experience a significant build up that creates strange noises when water is heated in the system. This can usually be flushed out by an engineer but it could cause damage if left untreated.
  • Discoloured hot water

    If the water that leaves your taps is discoloured or smelly after it is heated, this may be a sign that the anode rod inside has become defective and needs to be replaced.

How long does a hot water cylinder usually last?

Hot water cylinders today typically come with a minimum 25 year guarantee but can last longer if maintained well. Your boiler engineer will be able to carry out comprehensive checks for you to see if the hot water tank needs replacing.

Summary

  • A hot water cylinder is a tank used for storing hot water for later use. The two types of hot water cylinders available in the UK are pressurised unvented hot water cylinders and vented hot water cylinders.
  • Unvented hot water cylinders receive cold water from the mains, while vented hot water cylinders use an external cold water tank often stored in the attic.
  • The advantages of a hot water cylinder include its suitability for larger homes and its ability to store hot water. With smart controls and green energy it can be cost effective, whilst more complex to install.

Installing a hot water cylinder in your home?