07 December 2020
Free guide to hot water cylinders

Free guide to hot water cylinders

This guide will help you understand how hot water cylinders work, how to get the best out of them, and how to diagnose common problems.

Any home that has a regular boiler (or ‘system boiler’) requires a hot water cylinder to store the hot water that the boiler produces. A water cylinder plays a vital role in providing your home with hot water.

Hot water is something we tend to take for granted and expect to be available ‘on tap’ whenever we need it. If you have a combi-boiler, you will be used to having hot water on demand day and night. If you have a conventional or system boiler, you will expect a supply of warm water to be available for bathing, showering or washing up.

Discovering that you suddenly don’t have hot water on tap in your home is both inconvenient and worrying, especially during the colder months. This article will help you understand, identify, and put right any problems with your hot water cylinder.

What kind of hot water cylinder do I have? And how does it work?

The first step in diagnosing an issue with your water cylinder is to work out what cylinder you have.

Unvented hot water systems

An unvented hot water cylinder is a water vessel that holds heated water under pressure, releasing it when a hot water tap is opened and providing instant hot water. The name comes from the fact that the system is pressurised and so doesn’t need to vent steam or water.

Unvented systems have been fitted in homes since 1986 and are more popular than vented cylinders. The high pressure available from an unvented system means large quantities of hot water can be pumped around the system at a steady, regulated flow. Ideal for homes with multiple showers.

They tend to be more expensive to install than traditional vented systems because of the extreme pressure they operate under. Additional safety features, like relief pipework, need to be installed, they need to be fitted and maintained by specially qualified technicians with G3 qualifications.

Vented hot water systems

Popular in older homes, vented hot water systems require a cold water tank which is usually located in a loft or attic. This tank feeds cold water to a hot water cylinder. The cylinder is typically situated in an airing cupboard, with the cold water feed at the bottom of the tank. Heated water rises to the top of the reservoir where it is drawn off for feeding the heating system.

There are two methods of heating water with vented hot water systems:

  • Direct heating: Immersion heaters and/or a gas boiler is connected to the system and provides the hot water to the cylinder
  • Indirect heating: A coil within the hot water cylinder is fed via the central heating system and heats the water in the cylinder. An immersion heater is also provided so that the boiler can be switched off in the summer and the cylinder takes over providing hot water

Common problems with hot water cylinders

The following issues are the main problems we see with hot water cylinders. While you can identify and even fix some of these issues yourself, in most cases, it’s best to contact a Gas Safe engineer first.

Lack of hot water

Check your electricity supply

A water cylinder that isn’t delivering hot water may not be getting power or may have tripped a switch on your electricity meter. Check the circuit breaker as the first step to make sure it hasn’t tripped and that you’re getting electricity to your home. If it has tripped and your supply is on, try switching it off and then on again.

Check your boiler is igniting

If your central heating system is powered by a gas boiler, then you need to check that the boiler is igniting. If the pilot light is out and it won’t reignite, you will need to contact a Gas Safe registered engineer.

Check your boiler for error codes

Your boiler may be showing an error code on its display. To find out what the error code means, consult your boiler’s manual or contact us for assistance using our online contact form. Some boiler error codes can be easily rectified with a simple boiler reset.

Check your boiler’s pressure

If your home runs on a combi-boiler, then low pressure may be the reason for your lack of hot water. The correct water pressure for a home combi-boiler is around 1.5 bar. Your boiler should have a gauge that’s easy to see.

If the pressure is below the normal range, you will need to repressurise your boiler. Please be sure to check your manual before attempting this. If there are no instructions or you are unsure about doing this yourself, please get in touch with our friendly team for advice.

Check your boiler’s temperature settings

Also check that the hot water is set to a reasonable temperature on your boiler’s settings / control panel.

Check for leaks

A leak in either your heating or hot water system can cause a fall in pressure and result in a lack of hot water. Leaks can also cause damage.

Leaks typically occur at joints in pipework. Check the pipes around your boiler and hot water cylinder. Look for damp patches, mould or peeling paint on ceilings and walls too.

Incorrect timer control panel settings

Another factor to consider before calling an engineer is to check your control panel settings. This may have been affected by the clocks changing, issues with your power supply, back-up batteries failing or even someone altering the settings without your knowledge.

It should be easy to see if your boiler is currently active for hot water on the timer control panel. If you are not sure, you can check your manual or contact us for assistance.

Inadequate Hot Water

Cylinder size

If your water heater is producing hot water, but not enough of it, it could be too small to meet the household's hot water demand. Your cylinder may simply not be big enough to meet the demand.

In the long term, it may be more cost-effective to upgrade to a larger boiler and hot water cylinder. Your system may need to work hard to heat the water you need, especially during colder months. One of our home heating experts will be able to advise you on the most appropriate boiler size for your home, based on your current and future usage.

Heating element failure

If your unit is not undersized or it suddenly produces less hot water than it used to, one of its heating elements may have failed. A constant supply of lukewarm water during a shower is a typical sign of a defective upper heating element. Hot water that runs out quickly during a shower is a sign of a defective lower heating element.

Your water is too hot

Too much hot water can be almost as frustrating as not enough hot water. Before you try anything else to solve this issue, make sure that the temperature has been turned down on your boiler and control panel.

If the water is still too hot, then there could be an issue with the temperature pressure relief valve not shutting off correctly when it reaches the set temperature. This fault can be particularly dangerous as steaming or boiling water could start coming out of your taps.

Contact a heating engineer to repair or replace your pressure relief valve. You will also need a heating engineer if there’s any sign of boiling from within the cylinder. It's also possible that one or both of your water heater's thermostats is set too high; an engineer can check this for you by checking the thermostat settings under the access panel on your hot water cylinder.

Rusty or smelly water

If your water comes out of the tap with a brown, yellow, or red tint to it, there could be corrosion inside your water heater tank or in the pipes in your home.

If your water comes out smelling like rotten eggs, there could be bacteria in the hot water heater tank. In either case, contact a heating engineer for assistance.

Strange noises from your water cylinder

Water in your cylinder expands as it’s heated, so the odd creak or gurgle from inside is perfectly normal. However, noises that have become increasingly frequent or louder are something to investigate.

Unusual noises coming from your hot water cylinder could be a sign of sediment or limescale build-up. This build-up can create blockages and lead to leaks. Excessive build-up of sediment in the bottom of the tank can cause the bottom of the tank to overheat, boiling the water. This can create more noise than usual.

Regular powerflushing and servicing by a professional engineer will help to prevent this build-up, removing any blockages and keeping your heating system flowing nicely.

Your heating system needs a service

Just like your boiler, your hot water cylinder must be serviced by a central heating expert each year so it can perform well and have a long lifespan.

The best way to avoid a nasty surprise with your hot water supply is to ensure your heating and hot water system is regularly maintained by a qualified professional to help keep everything running safely and smoothly all year round.

Servicing your hot water cylinder can help prevent significant issues by spotting small problems like leaks, corrosion, loose heating elements and faulty parts.

Need some water cylinder advice? We’re here to help

Our experienced heating engineers can perform assessments of your heating system to identify potential issues and help extend the longevity of your hot water cylinder. We also supply and install new, efficient hot water cylinders for homes and businesses right across the East Coast of Scotland.

Call our friendly team on 0800 3899 463 (Mon to Fri, 9am to 5pm) for help, or use our online enquiry form.


Written by Kingdom Gas Services team