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Misunderstood! Thermostatic radiator valves are actually amazing!

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Many people misunderstand how thermostatic radiator valves work.

When used in the right way, they have a BIG role to play in keeping down bills.

Used in the right way, they save around 18% on average or £180 a year for the average home (based on testing at Salford University).

They are extremely good at stopping rooms from being heated more than you really need. Even a room just being a degree or two warmer than you really need is wasting money.

Position 3 on most valves will limit the maximum temperature in a room to around 20C.

Position 5 will mean the radiator will try to heat a room to 28C....and even if it never gets that hot it will waste significant amounts of energy trying to get there.

Only ever make very small adjustments on the valve. If you aren't warm enough, cranking it right up won't make the room warm up any more quickly.

This article tells you in simple, practical terms how to use these clever devices, along with some things that might surprise you.


This is one of my most valuable web pages for saving you money and energy.


Some facts first

What could be better than a simple, low-cost device that WILL automatically and precisely control the temperature in a room, no matter what the weather, so you don't overheat it unnecessarily?

Thermostatic radiator valves are designed to do just that, when used properly they will keep your rooms cosy and they’ll also be more economical to run without wasting vital energy.

A recent Best Heating survey revealed that 62% of householders surveyed said they don’t know what the valves on a radiator do!

A study by Strathclyde University showed that if thermostatic radiator valves are used as they should be, with doors and curtains closed in winter, it would save between 10% and 30% of gas usage.

Thermostatic radiator valves (TRVs) are incredibly clever devices, able to control room temperature very accurately! I've actually taken measurements in my home and was impressed! They really are 'thermostats'.

Here are the basics, followed by some invaluable tips.

All TRVs have some sort of scale on them. It is usually just a simple number scale, though on some very small fancy ones the scale really is not that obvious at all.

Setting 3 will actively manage the temperature of a room to around 20C, and is an ideal starting point when setting the comfort for any rooms.

Most people prefer around 18C for bedrooms and sleep comfort, so between 2 and 3 on the valve. For a living room, where 22 or 23C is usually preferred, the setting would be 3 and 4.

Everyone is different, of course, and valves do vary a little from manufacturer to manufacturer. This also assumes that radiators are sized and setup correctly for the rooms they are in and the boiler is setup correctly.

As you can see in the table above, setting a thermostatic valve at number 5 is asking the radiator to heat the room to 28C, which is FAR higher than most people would ever need or want.

On setting 5, the heat is effectively fully on with no control, and makes the room feel like an OVEN!

The best way to use these valves, to give you the comfort you want and avoid wasting energy and money, is:

  • Start out with them set at number 3, while you get to understand how the valves work and your own comfort zone

  • After the heating has been on a while, if a room isn't at the temperature that is right for you, only make SMALL adjustments up or down. This raises or the lowers the temperature by JUST a degree or two, to nudge the room warmer or cooler. If a room isn't warm enough, DON'T be tempted to turn the valve up to maximum, as this will tell the valve that you want the room like an oven at 28C. The next thing you know, you will be opening windows, and pouring heat and money out of the house!

  • Industry experts all say that turning the valve up to maximum WON'T make any difference to how quickly the room warms up.

  • If a room is too warm when you walk into it, and the valve is set higher than you normally have it, DON'T just turn the valve off. Just adjust it down to the number you normally use for that room. The valve will stop the flow of water to radiator until the room has dropped to that 'normal' temperature, which it will then maintain.


Other energy saving tips

  • As shown the photo above, ensure the finger rings holding your valves haven't worked loose. If they have, there will be tendency for the radiator to overheat the room, as the valve can't do its job properly. They are very easy to tighten by hand and have no fear, it is impossible to cause any problems. You don't and won't need a plumber.

  • If you have a favourite temperature for a room, mark it with a felt tip pen as shown in red in the photo above. Then, if someone adjusts the radiator away from this for some reason, you know exactly where to put it back to.

  • Alternatively, mark up your TRVs in the way I have this one below.

  • If you aren't using a room regularly, turn the valve completely off. For most homes this is probably the best thing to do to save energy. There will be exceptions to when this is best but I won't try to explain those here.

  • If you turn a thermostatic radiator valve OFF, have NO fear of causing freezing pipes. ALL TRVs have a built-in protection feature to stop this happening: if a room becomes extremely cold, the valve will actually open up and let some hot water through. (This is why they have a snowflake symbol!)

  • The chances of having freezing pipes are actually extremely remote these days. This is because:

    1. although often not as well-insulated or draught-proofed as they need to be, UK homes are far better insulated than they were 50 or 60 years ago, and most have double glazing.

    2. freezing pipes are most likely in homes with no central heating and unheated garages, outbuildings and annexes.

    3. freezing only occurs in weather conditions where there are extended periods of sub-zero conditions if you have pipes in extremely exposed locations such as lofts or dormer rooms with pipes that actually go into unheated spaces behind the scenes. Extreme sub zero weather spells are becoming increasingly rare, and will be rarer and rarer, as winters become milder with climate change.

  • If you DO have TRVs, don't adjust the small valve at the other end of the radiator. This valve is called the lockshield valve and is something that should only be adjusted by a central heating engineer when setting up a system.

For info, some valves have a 1-6 scale, but all the same rules apply.


But what about the main heating thermostat?

This section is for when you have a fixed wall thermostat (such as in your hall). If you have a wireless thermostat that you move around, it is a little different. I'll be adding a section on wireless thermostats soon.

The thermostatic radiator valves in each room limit the MAXIMUM temperature in each room so each room is never heated more than you actually need.

The main house thermostat has overall control directly of the boiler and the overall warmth of the house.  

As the central one controls the boiler if it is set too low the boiler will think the house ‘as a whole’ is as warm as you want it to be and the heating will switch off, or stay off.  

My suggested way to get things set up the way you want and make both types of thermostat work together is as follows:

  • Set all the thermostatic radiator valves at position 3, so around 20C. If you know there are rooms you will want a little warmer than that, then set them a little higher. Similarly if you know there are rooms you will want it a little cooler (say bedrooms) set them slightly lower than 3.

  • Crank the central thermostat up to full, then let the house and rooms get up to temperature for an hour or so.

  • Adjust the valves in each room a small amount up or down to get them to the temperatures in each room just as you want them.

  • Again, wait a little while for the temperature in each room to adjust (at least half an hour).

  • Now you should have the rooms and the house in general at temperature you want.

  • SO, final step then is to turn the central thermostat down until the boiler ‘just’ clicks or switches off. 

This might seem a little long winded but it is definitely worth doing. It’ll give you the comfort you need with minimal wasted energy. It might take a little trial and error with all the thermostats.

A really important thing then is to only make very small adjustments on any of the thermostats and always give the rooms or the house some time to respond.   

You’ll also probably find in time you need to make further adjustments such as in very cold or damp weather. This is not necessarily because the house will be cooler but because humans feel comfort in quite complicated way. If you’ve been outdoors and just come in, or have been doing exercise of any sort it can affect how comfortable you feel indoors soon after.  

Changes in indoor humidity also affect how comfortable you feel. Different humidity levels can fool the body into thinking you feel cold at 20C one day when you didn’t the day before in the same room at 20C. 

As the central thermostat has overall control of the boiler if you have a TRV.

If anyone knows of any better approaches to the above do let me know.


But what about boiler temperatures? How should I set these in relation to my radiator valves?

You may have heard something about being able to improve your boiler efficiency if you lower the temperatures on your boiler.

My other blog explains this, and how you can do this yourself. It saves £80-£100 on the average gas heating bill.

It is probably best to do all the above stuff on thermostatic radiator valves first. Get to know them, get them how you want them, and only then go on to adjust your boiler temperatures.


Troubleshooting thermostatic radiator valves that don't seem to do what they should!

Do you have a radiator that is either hot or cold ALL the time the heating is running, no matter WHAT position you set the thermostatic radiator valve at?

If so, this other article will help you diagnose and very easily fix the two main causes


If you don't have thermostatic radiator valves

I would urge you to get them fitted asap. You only want to heat the rooms you use, to the level that you want when you are in them.

Without these valves, the control of heating in a home is extremely crude, and you have very little ability to properly set or change the temperatures in each room to suit your needs.

The valves themselves only cost £10 or so, but you will need a plumber to fit them.


Do you wonder why you have TRVs on all radiators except on one radiator?

This is usually deliberately done by a central heating engineer. Most central heating boilers and pumping systems need to have at least one radiator in the house that they can always circulate water through when the heating is on.

If you had a TRV on every radiator you could have a situation where all the rooms are warm enough and all the TRVs have shut off the water to all the radiators. The boiler and its pump would not then be able to circulate water, potentially leading to boiler overheating issues.


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Mark Thompson

Geeky footnote point. The above all assumes a radiator is the correct size for the room, a system is balanced properly and that boiler and other system settings are as they should be.

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You have shared a great information i have also read this type of great information on



Our house in the SE of the UK is unoccupied in the winter. The heating is on constant and I have set system stat to 12C, as required by our insurers, and TRVs are on 1. Is this good enough to keep pipes from freezing or could I reduce the level? Double glazed throughout with insulation in the loft where the water tanks are located.

Mark Thompson
Mark Thompson

Apologies for the late reply. The alerts I get from the web site were going into my spam folder. The answer is most probably yes. I know someone in a 100 year old semi without heating and the temperature in her house never actually goes below 10C in winter. Pipes are typically only prone to freezing if they are not well insulated and in exposed locations such as lofts, or under suspended downstairs floors or in other odd locations like behind panels in dormer bathrooms or loft conversions (where they can be exposed to cold draughts from attic areas). Even then outdoor temperatures typically need to be below -5C to cause any problems at all.



I don't have a wall thermostat just a dial on the boiler and I have that set to eco, all TRVS downstairs are set at 5 and it s hot but I only have my heating on for 1hr on morning and 1hr early evening, is there anything I should do to reduce consumption



Thank you very much. I need two fitting .



I like to think I understand how it works, by intuition rather than actual numbers! But just for my own peace of mind, can anyone tell me if what I'm doing is right?

Our upstairs has 5 bedrooms and a bathroom. The bedrooms are laid out along the landing which is long and narrow. We have a thermostat on the wall at one end, outside of 2 of the bedrooms. Then there are 2 more bedrooms, then a radiator the other end, on the opposite wall, and next to that is the master bedroom which is about twice the size of the smaller ones.

I have trvs on all except the bathroom rad which is a towel rail. I set…

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