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Jenny’s water can’t handle the heat

Jenny’s water can’t handle the heat

Jenny’s hot water cylinder can’t provide enough hot water for her entire shower. Save money & improve water pressure while reducing your water bill

Guide to hot water cylinders

water tank with jacket

If you are considering the purchase of a new hot water cylinder, there are some basic facts that will help you decide which one is right for you. Hot water cylinders are available ‘vented’ and ‘unvented’, and we explain the difference between the two.

Vented hot water cylinders

This type of water cylinder needs a water storage (header) tank to store water piped in from the mains. The tank is usually installed in the loft (or in the highest point in the property) and the system relies on gravity to create a reasonable pressure for the hot water to circulate throughout the property.

The pressure of the water is dependent on the height of the tank above the relevant tap/outlet, so you need to take this into account as upstairs showers and baths will have lower flow output than downstairs. In fact, you may need a booster pump to overcome the water pressure problems that can occur.

Vented cylinders are easier to install than unvented, but they do need a vent pipe to deal with water expansion issues. Households most likely to benefit from vented water cylinders would be properties with an electric shower only, no bath and just one or two people living there.


gledhill cylinder

Unvented hot water cylinders

With this type of cylinder there is no need for a storage tank as water comes straight into the cylinder via the water mains. Mains pressure means gravity feed does not apply, so the cylinder (minus storage tank) can be positioned virtually anywhere at any height, and you get a much more powerful flow than from a vented system. Also, you don’t have to worry about water freezing in a header tank during very cold snaps.

In an unvented installation the system won’t suffer contamination because it is sealed and bypasses areas were impurities could get into the water. With regards to water expansion, the unvented cylinder has either a permanent air bubble infused at the top of the cylinder, or a fitted expansion vessel.

Both vented and unvented hot water cylinders can use either direct or indirect heating systems. With the indirect method the cylinder is heated by a gas boiler or other external source. Hot water passes from the heat source through a copper coil built into the cylinder. In this case it’s a good idea to fit a reserve emersion heater in case of boiler breakdown, so you still have hot water.

The direct method involves one or two heating elements inside the cylinder that heat the water directly. Using the two element option can be very cost effective because it is specifically designed to be used with the Economy 7 tariff - one element for peak day time use and one for off peak where the water is heated cheaply at night and used when needed.



When should I install a new hot water cylinder?

  • If you get constant leaks or breakdowns it could work out cheaper to replace rather than to keep repairing. Your new boiler will be much more energy efficient and could pay for itself quite quickly.
  • If you have a big family or use lots of water a new professionally fitted boiler will be sized correctly for your needs, which may not be the case at present.
  • If you have an old boiler with a red jacket you will be paying higher energy bills than you need to. You would be better off upgrading to a new cylinder and better tariff. The off peak tariff in conjunction with the two element cylinder could save you lots of money.
  • If your water pressure is low and it takes forever to run a bath or the shower is just a dribble, a new unvented hot water cylinder will give amazing improvements.

Benefits of upgrading to a new hot water cylinder

Further benefits of installing a new hot water cylinder include:

  • Much faster heat up time.
  • Super insulation meaning less energy needed to maintain heat.
  • Stainless steel construction that will eliminate any future rust or corrosion.
  • Long guarantee for peace of mind (up to 25 years).
  • A holiday mode setting allowing shut down and restart of up to 30 days.

By choosing and installing the right hot water cylinder for your needs, you can enjoy more convenience and reliability, and cheaper energy bills.

Frequently asked questions

My hot water cylinder has no jacket, is this normal?

In the past, when a hot water cylinder and the cost of heating water was cheaper, it was normal not to have a jacket. This was because a hot water cylinder in an airing cupboard would also dry towels and clothing. However, red jackets that wrapped around a hot water cylinder became commonplace in the late 1960s. People believed this would save heat and make heating costs cheaper, and red jackets were used for the next 30 years. Afterwards, red jackets were replaced by the foam jacket as this was cleaner, better looking and would save more heat.

Why are hot water cylinders insulated?

Hot water cylinders are insulated to save on cost. Insulation makes the cylinder more efficient and the hot water last longer. Therefore this reduces the need to heat up the cylinder again for hot water.

What is the small box strapped to the side of the hot water cylinder for?

The small box is known as the “stat”. When the hot water reaches its desired temperature, the stat sends a message to the diverter valve or the boiler to switch off.

Why do I have green on my cylinder?

Copper corrosion is the cause of the green on your hot water cylinder. The corroding copper is most likely the result of an acid attack of flux or there is water surrounding the area. Copper corrosion may also be the result of a high amount of moisture in the air.

How do I know if I require a new hot water cylinder?

You should consider replacing your hot water cylinder if it is leaking water, but drying at the same time. Leaking water can get worse over time and cause damage. Small leaks can be hard to detect so you should always check for any damp patches surrounding a hot water cylinder. Consult your plumber or call Greenvision Energy if you are unsure about whether your hot water cylinder has a slow water leak.

Where can an unvented hot water cylinder be installed?

It can be installed in almost any location – the garage, upstairs, downstairs, loft or even in a basement. An unvented hot water cylinder needs a safety discharge pipe. Therefore in some basement locations, a sump and pump may be required.

Who can install an unvented hot water system?

You should only have an unvented hot water system fitted and serviced by a qualified person holding a current G3 Unvented Qualification. All installations of unvented hot water cylinders have to be notified to Building Control as required by Building Regulations. If your installer is a member of a Competent Persons Scheme, this will happen automatically and you will receive a Building Regulation Compliance certificate.

How long does a hot water cylinder last for?

A hot water cylinder should last for more than 20 years if fitted correctly and to the highest standard. However, the life expectancy of a hot water cylinder can be shortened by water leaks.