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What are thermostatic radiator valves (TRVs)?

The BestHeating guide to thermostatic radiator valves

We’ve written about them before – and the chances are that you are quite familiar with them – but what are thermostatic radiator valves (TRVs) and how do they work?

In this guide, we’ll delve a little deeper into the world of TRVs, looking at how to operate them and why you find them on the side of radiators up and down the UK.

This is the BestHeating guide to thermostatic radiator valves.

What do I need to know about thermostatic radiator valves?

A Pair of thermostatic radiator valves

Thermostatic Radiator Valves are probably more commonly known as TRVs and their main function is to control the air temperature of a space by automatically adjusting the amount of hot water that enters the radiator they are attached to.

A TRV will allow you to have a little more control over the temperature in each room of your home, making creating a warm and inviting space more efficient and cost-effective.

If you set up a thermostatic radiator valve in the correct way, it will allow you to create different heating zones throughout your home, despite only having one centralised boiler system providing your main source of heat.

In short, TRVs are a simple and affordable way of controlling the heat output of a radiator and the temperature of a room.

How does a TRV work?

A Thermostatic Radiator Valve is self-regulating and works by automatically changing the flow of hot water that comes into your radiator at any one time.

It is a pretty simple mechanism to understand and consists of two main parts – the valve head and the valve body – with the head (as you might expect) sitting on top of the body.

woodern thermometer on wooden surface

When the temperature of the room begins to change, a capsule in the head of the TRV will either expand or contract – automatically moving a pin in the body of the valve which causes the valve to either open or close.

If the temperature in your room drops a little too low, the capsule will contract and pull out the pin; allowing more hot water to enter your radiator and increase its temperature.

thermostat turned off

Conversely – if the room begins to get a little too warm – the expansion of the same capsule will cause the pin to close the valve and reduce the amount of hot water.

The capsules in thermostatic radiator valves operate using a metal spring that is filled with wax or liquid – with the liquid type considered to be the best and most consistent at adjusting the temperature.

One of the main advantages of liquid TRVs is that they are far more responsive to fluctuations in temperature than their wax cousins.

Wax can be quite slow to expand and contract, while liquid TRVs will change the flow of water into the radiator considerably more quickly – this is also reflecting in the price of both variations.

How much does a thermostatic radiator valve cost?

A standard pair of TRVs will set you back about £20, whether you buy them from our store or decide to shop for them somewhere else.

As with most things, prices vary depending on the style of radiator valve you want to buy and – with thermostatic valves – whether they are liquid or wax filled.

But the cost of the TRVs alone is not exactly an accurate representation of how much these radiator valves will set you back – not when you factor in installation costs as well – so it’s important to look at what you may need to pay for to add some to your radiator.

work tools on the floor

Fitting any new radiator valve could mean that you need to drain down your heating system – either partially or in its entirety – so if you need to do this for any other reason, it’s probably a good time to fit TRVs to your radiators.

Draining the system down and fitting TRVs to each radiator – let’s say there are about 10 in total – should cost about £350, if the engineer supplies the valves too, as it is a job that will probably take all day.

If you only have one pair of valves to fit, the engineer will probably just freeze the pipework and add the thermostatic radiator valves to the radiator. This should set you back (including the price of the TRV) about £120 – or whatever the going rate for half a day’s work may be where you live.

Are thermostatic radiator valves worth it?

Now you may be sat there musing to yourself: “I already have a thermostat that controls my heating, so why would I go to the trouble of buying a set of thermostatic radiator valves?”.

But the beauty of a TRV is that you can set a different temperature in any room of your home, meaning you don’t have to undertake the tedious task of adjusting the room thermostat when it gets too hot or too cold.

For example, if your current system contains a centralised boiler that provides heat and hot water and you have a single wall thermostat, the chances are you are heating rooms that aren’t occupied.

With well over half of the energy in your home being used for heating and hot water, if you combine a TRV with a complete set of heating controls – including timers and room thermostats – you can make substantial savings on the overall cost of your heating.

Energy savings to be made with thermostatic radiator valves have been estimated at as high as 40%; however, these figures do depend on many variables, including radiator efficiency, insulation and where the TRVs are installed.

The trick is all in how you ‘zone’ your home’s heating system.

a graphic illustrating the ideal temperature for each room of a standard UK property

Most people have the temperature in their living room set to a comfortable 21-22°C – that way, when they’re settling in for a night in front of the gogglebox, they are nice and cosy.

But a bedroom that has the heating cranked up to more than 20 degrees is going to be far too stuffy for even the coldest person to get comfortable in, and this is where the TRV comes into its own.

Controlling these different zones in your home allows you to be more efficient with your heating. Setting each space to a separate temperature will save you money and there will never be a time when you unnecessarily heat a space that isn’t being used.

Can I install a TRV in every room?

Building Regulations do state that the heating systems in domestic dwellings have a minimum set of controls.

For a system that uses a combi (combnation) boiler, this is done with a timer or room thermostat and the different heat settings of individual rooms are generally achieved using TRVs.

A man turning a thermostat on

Standard practice is to leave one radiator without a thermostatic radiator valve installed, and to leave that appliance permanently switched on.

If your boiler is fitted with a flow meter – that detects when all of your radiator valves are closed, you can install a TRV on every radiator if you want to.

You can leave any radiator without a TRV, but it makes more sense for you to select the radiator in the room with your wall thermostat.

As your main heating thermostat is directly linked to your boiler system – a link that you will use to fire your heating up or turn it down – having a TRV in the same space will mean that they fight to control how hot or cold your room will be – resulting in something of a Thermo-Spat.

In this instance, you could turn your wall thermostat up to get rid of the chill in the space, only to find that the thermostatic valve on the nearby radiator expands to close off the supply of hot water to the radiator, cooling the room and making the whole thing a pointless exercise and a waste of time.

This is one of the reasons that you often find a boiler thermostat in the hallway of a house.

In this space – that is very rarely heated to a constant temperature – it makes sense to leave your radiator TRV free.

After all, the hallway is usually a thoroughfare between downstairs and upstairs and is – more often than not – a space that doesn’t require a huge amount of heating.

really long hallway

It’s unlikely that you will spend a large amount of time in there – unless you have a huge decadent space – so going TRV free here will mean that other spaces can take all of the benefits – fitting your hallway radiator with a manual valve instead will mean that you can adjust its output according to the weather that day.

If you have a wall or room thermostat that controls your boiler system’s output in a room that you spend a lot of time in (like your living room or dining kitchen), its probably advisable to not install a TRV here, and if you already have one in that space, it may be worth your time to remove it and connect a simple manual valve instead.

Thermostatic radiator valve problems

Although they can prove to be pretty handy pieces of kit, TRVs are relatively primitive, especially when compared to the newer smart heating controls that are available on the market.

Their simplicity, though, does mean that it shouldn’t be too difficult to diagnose any problems, should they start to fail you, which they sometimes have a tendency to do.

An H block valve TRV fitted to white pipework and set to number 3

The most common and regularly occurring problem with a thermostatic radiator valve is that the valve – or the head of the valve – begins to stick or catch.

This will leave them open or closed and can happen when the setting on the valve has not been adjusted for some time – such as at the end of a long hot summer.

This is a pretty simple fix and shouldn’t result in you having to part with any extra cash – provided that the pin in the valve hasn’t failed and the valve head isn’t totally immovable.

What you need to do is to turn the TRV to its highest setting – this is usually displayed as a number 5 – to fully open the valve and then remove the top of the TRV by undoing the large thumbwheel just above the radiator tail (this should be pretty easy to do and is most likely not to require a wrench to achieve).

Once removed, you should be able to see a little metal pin that would normally move up an down.

If this happens to be a little stiff – and is preventing the valve from opening an closing correctly – simply give it a spray with some trusty WD40 and work it up and down a few times to try and loosen it up a bit.

If all appears to be ok with the pin, it could be that the wax or liquid cartridge at the top of the TRV has failed and you will need to purchase a new thermostatic radiator valve head.

If the pin in the valve won’t budge, forget it, you’re going to need to buy a new set altogether, and you will need to drain down your heating system.

My TRV isn’t working properly

If there are ever instances when you think that your TRV is not operating correctly, these issues can normally be fixed with some minor adjustments.

It can sometimes be the case that a draught is causing the TRV to think that your room is colder than it actually is – this is particularly common if you have a door near to your radiator.

Conversely, the TRV may be blocked by a piece of furniture, so the wax or the liquid that determines when the pin rises and falls to adjust the temperature won’t be able to operate correctly.

Therefore, it is important to ensure that you do everything you can to ensure your TRV is positioned correctly and isn’t being unduly affected by other influences stopping it from operating at its best.

A picture of a radiator cover with a little door for the TRV

As in the image above, this radiator cover is arguably stopping the TRV from operating at its best, as it is blocking any draught or airflow to the valve, this could lead to the valve not operating correctly and the space not heating up as well as you may like.

In this instance, it may need you to undertake a few separate tests to ensure that you get hot and cosy radiators when the cover is in place.

Believe it or not, the most common cause for a thermostatic radiator valve to not be working correctly is because it has been set to the wrong number or turned off entirely.

The valves are set by turning the control knob to the desired setting to achieve the desired room temperature – anti-clockwise to increase and clockwise to decrease.

Now, rooms can take a while to heat up so ensuring your TRV is set to the correct temperature setting isn’t an overnight process, it could take a few days to get right.

To do so, open the valve fully, turn your heating on and let it run for a while to be sure it has stabilised. If at this point you feel your room is too hot, turn the TRV down by one mark and then check the temperature again the following day.

If you feel that your room as gotten too cold, simply unscrew the valve by one mark and repeat this process until the temperature is correct and comfortable.

What do the numbers on a TRV mean?

Contrary to popular belief, the numbers on your TRV do not represent specific room temperatures, because as I have mentioned, the temperature at which the valve operates depends on water temperature, the airflow around the valve, the size of the room and the heat loss in that space through walls, windows and floors.

A hand turning a trv round to a different number

Therefore, it is not uncommon to have very different settings, in different rooms, to achieve the same temperature.

If you have a room that is heated by two separate radiators, there will be an interaction between two TRVs, competing to be in charge of how hot or how cool the room is.

If you have this in any space, it can be a bit fiddly to get right, but you should always start with the valves at matching settings.

Then, if you find that the temperature is not even, try adjusting the settings on the valve at the coldest part of the room. Once you have this right – and like I say, it can be fiddly – the TRVs can then be adjusted together and you should easily achieve the optimum temperature in that space.

Things to remember about TRVs

To end, I just thought I would give you a quick overview of things you need to keep in mind about thermostatic radiator valves –

  • TRVs sense the air temperature around the radiator and adjust the heat output accordingly.
  • They can be wax or liquid-filled and will expand or contract based on the ambient temperature of a space.
  • In order to ensure that they are working correctly, it is important to ensure they are not blocked by furniture and curtains.
  • You can expect to pay around £20-30 for a good value TRV.
  • You could install it yourself, or have a professional do it.
  • They CAN and WILL help you to save money if you use them intelligently.
  • You probably shouldn’t use them in bathrooms and definitely shouldn’t place them in the same room as your boiler thermostat.
  • We have an amazing range of thermostatic radiator valves at BestHeating.com

So there you go, that was our quick guide to TRVs and how to make the most of having them alongside your new radiator. I hope you found out what you needed to. Till next time…

Frequently Asked Questions

Thermostatic radiator valves, or TRVs, are designed to automatically shut down and prevent the flow of water through the heating system in warmer weather, so they need to be carefully maintained in the hot summer months.

If TRVs are turned down low when the weather is warmer, a few months of inactivity could lead them to become stuck in the ‘off’ position.

As a result, when the weather cools down again, you might find that radiators accompanied by a stuck TRV will struggle to heat up and might not be able to – a plumber might even be required to fix the issue at an excess cost.

To avoid such a situation, open all your TRVs to full capacity by turning them in a clockwise direction during the warmer summer months.

For further information, take a look at our dedicated blog – Summer Heating & Radiator Tips.

It is not a good idea to fit TRVs to your bathroom radiator, simply because the TRV will not work properly. 

TRVs have their own thermostat to control the temperature of the room. So, the heat caused from having a hot shower or bath can confuse the TRV or shut it down completely. 

Not ideal if you were hoping to get wrapped up in a nice warm towel!

For more information on TRVs, check out our Thermostatic Radiator Valve Guide.


A thermostatic radiator valve, or TRV, can be fitted to a towel radiator, and will provide the exact same functionality is it does when installed alongside a standard designer radiator.

However, it is best not to install a TRV on a towel radiator in your bathroom, as the steam and heat from the bath and shower can cause the TRV to malfunction and not operate correctly.

Most modern thermostatic radiator valves are bi-directional – so can be fitted on either the flow or return pipe of your radiator.

However, it’s always best practice to fit the TRV on the flow pipe that enters your radiator.

If a non-bi-directional thermostatic valve is fitted to the return side of the radiator, it can make a loud vibrating noise when water tries to pass through it.

It’s best to check the product thouroughly before installation and look for flow indicators where possible.

To discover more about thermostatic radiator valves, take a look at our complete range of TRVs and learn why they’re important in our ultimate guide to TRVs.

You should replace your thermostatic radiator valves (TRVs), or at least upgrade the TRV heads, if they are 10 or more years old.

TRVs can decline in terms of performance and accuracy over time.

To learn more about what TRVs are and why they may be beneficial, check out our guide to Thermostatic Radiator Valves.

And, if you’re considering changing yours, take a look at our comprehensive Radiator Valve Guide.

Thermostatic radiator valves (TRVs) offer several benefits, assisting your radiators to operate in an energy efficient manner for long-term savings on your heating bills.

Find out more in our Advice Centre blog, What are Thermostatic Radiator Valves (TRVs)? or consult our Radiator Valve Guide.

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