How To Change A Thermostatic Radiator Valve

Author: Stuart Hunt - Published: 08.09.20
How To Change A Thermostatic Radiator Valve

When it comes to how to change a thermostatic radiator valve which is also known as a TRV, a thermostatic radiator valve allows you to control the heating output for each individual radiator in your home.

This step-by-step guide for how to change a thermostatic radiator valve will help replace and install them in a heating system.

  1. Turn off the water supply for the heating
  2. Connect a drain hose to a drain off valve
  3. Drain down the heating system
  4. Undo the two nuts on the radiator valve
  5. Remove and replace the radiator valve
  6. Re-tighten two nuts on the radiator valve
  7. Refill heating system
  8. Remove air from the heating system

As a plumber myself of over 20 years, I have changed hundreds of thermostatic radiator valves; therefore, I can guide you through the process.

How Much Does It Cost To Replace A TRV

An experienced plumber will charge between £75 and £100 plus the cost of the thermostatic radiator valve. In London, the price will most likely be higher with prices of £78 to £90 per half hour

If you were to change the thermostatic radiator valve yourself the cost will be much lower as all you will need to purchase is a TRV which will cost between £10 and £40 for a standard TRV.

If you want to purchase a smart thermostatic radiator valve, you will need to buy the radiator valve that goes with your room state or that is controlled on your mobile phone for more on smart heating.

How Long Does It Take To Change A TRV

A qualified and experienced plumber will change a thermostatic radiator valve within 30-60 minutes on average, some older heating systems can take longer due to removing air from the heating system

Combination boilers and unvented heating systems are the easiest to work with as they have pressurised heating systems.

Which Thermostatic Radiator Valves Are The Best?

Below is a table of four Thermostatic radiator valves that have been grouped together these include all the details of the radiator valve including a link to view each of the valves.

Standard 90 Degree Angled Thermostatic Radiator Valves
SettingsNo: 1-6No: 1-6No: 1-6No: 1-6
Frost ProtectionYesYesYesYes
Standard Straight Thermostatic Radiator Valves For Towel Rails
ManufactorHB SignatureRealmNRGHoneywell
Imageir?t=homeownersguide 21&language=en GB&l=li3&o=2&a=B075LKT3M7ir?t=homeownersguide 21&language=en GB&l=li3&o=2&a=B075LKT3M7ir?t=homeownersguide 21&language=en GB&l=li3&o=2&a=B075LKT3M7HB-SigntureRealm-TRVNRG-TRVHoneywell-VTL120-15S

When it comes to changing a thermostatic radiator valve, you will need to do a couple of things.

  • Find out which type of heating system you have
  • Find the drain off valve
  • Drain down the central heating
  • How to remove air from the heating system

Tools And Materials, You Will Need To Complete This Job.


  • Spanners
  • Adjustable grips
  • Drain hose or garden hose


  • Thermostatic radiator valve (TRV)

What Type of Heating System Do You Have?

There a couple of different types of systems these are:

  • Combination Boiler
  • Unvented
  • Gravity and pump

Gravity And Pumped Systems

If you have this type of system, typically you will have an airing cupboard with a big copper cylinder which can be green, yellow or blue in colour or if your hot water cylinder is ancient it may be just copper with a red jacket over the top.

Combination Boiler

You would have a combination boiler that controlled both your heating and hot water meaning you would not have an airing cupboard with a big cylinder; most combination boilers will be in the kitchen or the loft

For the best Combination Boiler, you can read our guide to the best Combination Boilers.


For these types of systems, you will have a big tube-looking cylinder which will be white or grey, typically the most commonly known unvented cylinders are:

  • Megaflow
  • Gledhill
  • Heatrae Sadia

For the best-unvented systems, you can read our guide to the best unvented hot water cylinders.

Turn Off The Water Supply For The Heating

Turning off the water supply to the heating system will depend on the type of heating system you have.

For Gravity And Pumped Systems – You will need to turn off your water supply for this type of heating system; you can turn off the water from your internal stop valve or the outside stop valve to your property.

For Combination Boiler – as combination boilers are completely a sealed system, you will not need to turn off your main water supply to your home

For Unvented Cylinders – Unvented heating system is similar to a combination boiler as they are both pressurised systems you will not need to turn off any mains water supply to your home.

Connect A Drain Hose To A Drain Off Valve

Once you have turned off the water you will need to find the drain-off valve, drain-off valves look like this:

Standard Drain Off Valve


Radiator Valve With Drain Off Built Into The Valve


With a drain off built into the radiator valve, you will need to turn off the radiator valve then using a bleed key slowly undo the square pin inside the drain off part of the radiator valve as shown below


Note - Be careful not to unscrew the gland of the drain-off valve, this is where the spindle goes into the drain-off valve.

If you don’t have a drain-off valve, don’t worry, I will tell you another way to drain down your heating system in a minute.

How To Drain Down The Heating System Without A Drain-Off Valve

The easiest way to drain water from a heating system without a drain of it is to go to the radiator next to the front or back door and then turn off both radiator valves on that radiator.

Bleed the radiator until the water stops then you will need the following:

  • Washing machine
  • Washing machine hose
  • Drain hose connector
  • PTFE Tape

First, turn off the washing machine valve and remove the handle

By unscrewing the screw in the front of the valve holding the little blue or red handle

Wrap PTFE tape around the 15mm tread on the washing machine valve.

Slowly using a spanner remove the bleed vent from the radiator that you have turned off next to the front or back door, then insert the washing machine valve into the radiator bleed vent and screw it in until tight, this should be fine to do by hand.

Connect the washing machine hose to the washing machine valve, then cut off the plastic end on the opposite end.

Connect the hose connector to the washing machine hose and then to your drain hose.

Reconnect the washing machine handle to the washing machine valve, then turn on the radiator valves to refill the radiator.

Open the washing machine valve then the radiator will start to drain the rest of the heating system from all radiators that are above the bleed vent.

The method above is excellent when you are changing a thermostatic radiator valve upstairs.

If you are changing a thermostatic radiator valve on the radiator on the same level as the radiator you are draining from you will need to remove the radiator from the wall and connect the washing machine hose directly to the radiator valve to drain that level.

Once the water has stopped flowing from your drain hose, you will then need to open the bleed vents from all over radiators to remove any extra residual water from your heating system.

Great, the water has stopped flowing, you are now ready to change a thermostatic radiator valve.

Undo The Two Nuts On The Radiator Valve

You can now remove the TRV head from the TRV body; which can generally be removed by unscrewing the retaining nut just under the TRV head.

Using adjustable grips, you want to place them over the top of the old TRV where you have just removed the head to grip the valve; this is so that you don’t damage the pipe when undoing the compression nuts on the pipework.

Using a spanner slowly start to unscrew the compression back nuts starting with the one attached to the copper pipework then the larger back nut that connects the thermostatic radiator valve to the radiator.

Now you are ready to remove and replace the thermostatic radiator valve.

If the back nut on the copper pipe looks ok, then you can leave the back nut and olive on the pipework and just put the new thermostatic radiator valve onto the existing back nut and olive.

However, if the back nut or olive does not look great, then you might wish to change them as well.

The best way to remove the olive from the copper pipe is to place your adjustable grips around the olive and twist slowly lifting the olive upwards to the top of the copper pipe until it comes off.

Note - Please don’t squeeze the grips too tight or you can damage the copper pipe.

If the olive doesn’t move, then you will need to cut the olive off the copper pipe making sure not to cut the copper pipe.

Once you have done up both back nuts to the copper tube and the radiator you will need to shut the drain off valve, then you are ready to start refilling your heating system, this is where the process changes.

Don’t forget you have opened the bleed vents on all other radiators! so, go around to each room and make sure that you have shut them

Advise - Turn off the drain-off valve but don’t discount your drain hose, just in case you need to drain down if you have a leak you are still connected to the drain valve

Refilling Gravity And Pumped Heating Systems

Turn on the water to your property so that the water starts to refill the heating system.

After a bit of time, you will need to start to bleed each radiator don’t turn on your heating at this point, or you will most likely burn out your heating pump.

Start bleeding each radiator starting from the top floor and working your way down until all the radiators are full of water checking the thermostatic radiator valve that you have just installed for leaks.

Once all the radiators are full, you can now turn on your heating to check all is working.

Once the heat is circulating there may still be some air in the system so just go around and check each radiator by bleeding them until you have water coming out of the vent.

That’s it; you are all done.

Refilling Heating System On Combination Boiler And Unvented System

To refill these types of systems I would recommend you read the manufacturer's guides as they can vary from each manufacture, but the principle is the same.

You will need to find the filling loop to allow water to flow into the heating system all combination boiler and unvented systems will have a pressure gauge which should be set to a maximum pressure of 1.5 bar this is typically indicated by a red arrow also there should be a green section within the gauge which also shows the correct pressure.

Remove Air From The Heating System

Once you have refilled the heating system and you have checked for leaks on the thermostatic radiator valve to you just installed you can now go around to all the radiators and start to bleed them to remove all the air from the heating system.

To remove the air, you should make sure the heating system is turned off so that the heating pump is not running.

Once you have removed all or most of the air from the heating system, you can then turn on the heating system and check all the radiators are heating up thoroughly.

If you find you have cold spots at the top of any radiators bleed that radiator again while the heating system is running.

If you find you have one radiator or more radiators that are not heating up you may still have air in the system, at this point, you will need to keep bleeding the radiators to air the rest of the air but bear in mind this may take some time to remove all the air.

If the boiler starts to knock or bang you need to turn off the heating immediately and allow the system to cool then begin to bleed the radiators again.

If once you have your radiators working but there is one radiator that is not heating up. Don’t worry; I have a guide that will help to fix that.

Final note – Some older heating systems can be troublesome when you drain them down with radiators not reheating or even just one radiator not working this is a problem even plumbers have.

An experienced plumber will have many different ways to get your heating system working again.

When you have a combination boiler or unvented hot water cylinder, you genuinely don’t get these types of problems; this is because they are pressurised heating system, which is the main water feed.

I have covered the basics for how to remove air from the heating system hereof which should get your heating back up and running however if you are still unable to get your heating system working you will need to contact a plumber as there may be a larger problem for why your heating is not working

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