How do radiator valves work? - a complete guide

How do radiator valves work? - a complete guide

Consider this your one and only guide in understanding anything and everything you’d ever need to know about radiator valves. Here at Trade Radiators, we wanted to provide our customers with a specialised guide which can help with every aspect of finding, buying, installing and maintaining the most appropriate radiator valve for your home heating system.

In this guide, we’ll help you understand why there are different types of valves, which sizes to buy for your radiators, how valves work, when you’ll have to change or buy a new valve, and other important radiator valve topics you’ll need to consider with any purchase.

Whether this is your first time buying radiator valves, or you’re looking to find out about how they work, and what you can do at home to make them perform without any issues, you’ll find the information you're looking for here.

What are the different types of radiator valve?

The two most common types of valve that you'll encounter in regards to your radiator are manual valves and thermostatic radiator valves (TRVs). Below you'll find a simple explanation of each.

Manual radiator valves

These are the simplest valves to operate and the most discrete to look at. If you understand a manual radiator valve, then you are practically a master with any heating system.

Manual radiator valves have a simple on/off internal system at play. You adjust them manually to let the desired level of hot water needed into the radiator. They are typically small valves that you twist to open and close.

Unlike a thermostatic valve where you can adjust the valve to a certain number and leave it alone, a manual valve requires you to get familiar with where a valve’s “sweet spot” is, so it may take a few attempts to the right temperature in every room. 

Thermostatic radiator valves (TRVs)

Now the most common type of valve to be installed in the UK, thermostatic radiator valves provide you with a level of flexibility that makes it easy for you to heat your space exactly as you'd like it. TRVs are generally made with a dial on top which can be turned from 1 to 5 and allow you to heat different rooms, or areas of your home, to different temperatures.

TRVs have become so popular because they allow for a level of heating micro-management that is not possible with the more simple on/off manual valves. Managing heating on a room by room basis by using thermostatic valves also improves energy efficiency (e.g by not overly-heating rooms that don't get used much), which is better for your heating bills.

How do thermostatic radiator valves (TRV) work?

Thermostatic radiator valves are designed to regulate the flow of hot water into radiators based on room temperature, rather than radiator temperature. TRVs contain a pin mechanism that controls water flow, which is influenced by a thermostatic element aon top of the pin. This element, often made of responsive metal or a wax canister, expands or contracts according to room temperature, adjusting the pin's position to allow more or less water into the radiator. This simple yet effective piece of heating automation helps to ensure you heat your room efficiently.

For a fuller explaination, please read our article How do Thermostatic Radiator Valves Work?

What do the numbers mean?

The numbers on the valve relate to the temperature of the room, not the internal temperature of the radiator, allowing for a specific level of water to enter your radiator.

For example, setting the dial to 1 will mean the radiator will only come on once the room temperature drops down below about 10°C. The radiator will come on and try to keep the room temperature around 10°C.  This is useful for a spare bedroom that isn't used much, but you don't want to remian completely cold.

On the other hand, turning the dial to 5 will cause the radiator come on when the room temperature drops below  about 30°C, which in the UK, means it will be coming on most of the time. Having your radiator constantly on to maintain such a high temperature all the time will quickly rack up your gas bills.

To find out the ideal setting and to learn more, please read our article What do the Numbers on a Thermostatic Radiator Valve Mean?

A white thermostatic radiator valve on a white, panel, convector radiator.A white thermostatic radiator valve on a white, panel, convector radiator.

Choosing radiator valves

When choosing new radiator valves for your radiator, it's important to consider your pipework and radiator placement. You'll need to look at where the pipe inlets are positioned on your radiator and if the heating pipes come out from the wall or up from floor. Knowing this is important as it will influence the type of valve you need to get for your particular set-up. Getting this right will ensure that your valve connects correctly to both your radiator and pipework, so below we provide an explanation of the three main types of valve.

Straight valves

Straight radiator valves are designed to connect radiators directly to the heating pipes in a straight line, making them suitable for installations where the pipes come up from the floor or directly from the wall behind the radiator. They provide a clean vertical connection that is a common sight when dealing with towel rails and some radiators which need to be hung higher up on walls.

Angled valves

Angled radiator valves are the most common type of valve required for a radiator. Anywhere your radiator has to make a 90° connection on the vertical plane, an angled radiator valve is needed.  Angled valves are often used when the pipes come up from the floor and need to bend to connect to the radiator. These valves have a 90-degree angle between the inlet and outlet, allowing for a smooth connection. A quick rule of thumb is this: If the right angle is up and in, you need an angled valve. If the right angle is out (i.e. protrudes towards you) and in, you need a corner valve.

Corner valves

While most radiators will see valves meet the pipework at a 90° vertical angle, corner radiator valves are made for use on a horizontal plane, i.e. when pipes come out from the wall and not the floor. Corner valves have a 90-degree bend to facilitate this connection

Valve sizing

The standard UK valve size is 15mm and, in the overwhelming majority of cases, this is the valve size you'll need for your pipework. However, this should not be taken for granted as some older houses could have 'microbore' pipes which can measure 8mm or 10mm, needing appropriately-sized valves. The best way for you to double-check is to measure the width of your pipes with a tape measure.

For more information, please read our article on Are Radiator Valves Universal?

Fitting, replacement and maintenance

When should I replace my radiator valves?

Radiator expert, Nic Auckland, says there are some tell-tale signs to look for when considering valve replacement:

"Like all components that are constantly in use, there will come a time when an old radiator valves wears out and begins to stop functioning efficiently.

One common indicator that a radiator valve may need replacing is if the radiator fails to heat up, despite the heating system being operational, which could be caused by a faulty valve failing to allow hot water into the radiator. Additionally, leaks around the valve or difficulty in turning the valve to adjust temperature settings are common signs of valve wear or damage.

These issues can arise due to corrosion, mineral deposits, or general wear and tear over time, necessitating the replacement of the valve to restore proper functioning and efficiency to the heating system."

How do I install a radiator valve?

Nic Auckland advises that fitting a new radiator valve yourself is not a task to be intimidated by:

"Replacing old, damaged or outdated radiator valves is a very common DIY job that can often result in your heating working much more efficiently. With a little DIY knowledge and confidence, replacing a radiator valve is defnitely something you can do yourself due to its straightforward nature and minimal requirement for specialised tools.

With clear instructions and basic plumbing knowledge, you can easily remove the old valve and install a new one to restore functionality to their heating system. Additionally, tackling this task can lead to significant cost savings compared to hiring a professional plumber, making it worthwhile for those looking to enhance their DIY skills and maintain their home's heating efficiency."

For more information, please read our guide on How to Replace a Broken Radiator Valve.


Can I replace my radiator valves without draining the system?

Wondering if you can replace a valve without going to the extra time and effort of draining your heating system down is a common question. If you're replacing valves on several radiators, it's definitely advisable to drain your system to avoid mess and complications. However, for a single valve replacement, draining may not be necessary. If you lack plumbing expertise, consider draining the system or seeking professional assistance. However if you feel confident, you should feel free to proceed with changing your valve without draining your heating system.

You can find out more details on how to do this in our section on How to Drain a Radiator Valve Without Draining the System.

Why is my radiator valve leaking?

According to heating specialist, Julie Boyle, there are several things that could be causing a valve to leak water:

"A radiator valve may leak due to several reasons, including worn-out or damaged seals, corrosion, or loose connections. Over time, the seals within the valve can degrade, leading to leaks around the valve spindle or body. Corrosion of the valve body or connections can also compromise the integrity of the seal, resulting in leaks.

In addition, loose connections between the valve and the radiator or piping can allow water to escape. That's why identifying and addressing the underlying cause of the leak promptly is crucial to prevent further damage and maintain the efficiency of the heating system."

Find the best way to check the integrity of a valve by reading our article What Can Cause a Radiator to Leak?

How should I maintain my radiator valve?

Keeping your valves in good working order is a sensible way of extending their life and ensuring your heating is functioning correctly and efficiently. It's worth inspecting your valves every now and then for any signs of leaks, corrosion, or damage, and address any issues promptly. You can also lubricate valve spindles and moving parts regularly to prevent stiffness or seizing up. Bleeding radiators periodically to release trapped air will also help  with heating efficiency and overall heating system health. Having a heating engineer come and perform yearly maintenance on your heating system is always a fantastic way of keeping on top of any issues.

If you've got specific issues with a TRV then be sure to read How to Repair a Thermostatic Radiator Valve.

Radiator valve FAQs

﹢ How can I balance my radiators using the valves?

Balancing a radiator involves adjusting the flow of hot water to achieve an even distribution of heat throughout the property. This typically entails partially closing the valves on radiators in rooms that heat up quickly while fully opening valves in cooler rooms, ensuring each radiator receives an appropriate flow of hot water to maintain consistent temperatures across the property.

You can read more on how to do this in A Complete Guide to Balancing Radiators.

﹢ Do heated towel rails need thermostatic valves?

Fitting thermostatic radiator valves to heated towel rails is certainly possible, but generally not recommended. TRVs regulate temperature based on the room's ambient temperature, whereas heated towel rails are designed to operate independently of room temperature, providing consistent heat for drying towels regardless of the room's warmth. The hot and humid nature of many bathrooms are not suited to TRVs, so it usually better to have manual valves on your towel rails, or even install an electric towel rail that can be controlled separately.

For a more in-depth explanation of this, please read Do Heated Towel Rails Need Thermostatic Valves?

﹢ Should valves be fully open?

Radiator valves should not be kept fully open at all times. While fully open valves would allow maximum water flow into your radiators, this would likely lead lead to imbalances in the heating system, with some radiators getting too hot and others staying too cool. Balancing the heating system by adjusting the valves ensures even distribution of heat throughout the property, making for a more pleasant living environment. By adjusting the lockshield valves on each radiator, you can control the rate at which water enters, ensuring more even warmth throughout all radiators in your home.

Feel free to read more in Should Radiator Valves Be Fully Open?

﹢ What is a lockshield valve?

Lockshield valves are usually located at the return end of a radiator, the other side from a TRV or manual valve. One of the main functions of the lockshield is to balance the flow of water that goes back to the boiler and the water that flows onto the next radiator in the chain. It's important for the evenness and efficiency of your heating system that the lockshield maintains this fine balance.

You can read more detail on this at What is a Lockshield Radiator Valve?

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