How to fit thermostatic radiator valves

17 January 2023

A plumber using grips to fit a thermostatic radiator valve to a radiator

A very important part of a radiator is the thermostatic valve. On the valve, you will normally find 5 settings that are achievable by twisting the valve. Depending on the situation, you should choose the setting you are happy with and the higher the number, the hotter the room.

Your valve & room temperature

When the room temperature has gone below your setting on the valve, the valve will open, allowing warm water to flow into the radiator, thus heating the radiator and the room. Once the room has reached the desired temperature, the valve will shut and stop water from going into the radiator. You may get a situation where you walk past a radiator and find that it is cold. That is normal and shows the valve is doing its job.

There is no need to change the setting on your valve after you've initially set it up. Leave it as it is and you should be fine. It is also important to note that the valve gauges the temperature by the testing the air immediately around it, so please do not cover the valve with a curtain or place furniture too close to it. A passage of air must be available around the valve for it to function correctly.

The video below is of a professional plumber explaining exactly how thermosttic radiator valves work.

Install your thermostatic valve

Now that you understand how a thermostatic valve operates, you may wish to install some on your existing radiators. In order to facilitate this, you will need a radiator bleed key, an adjustable spanner, a pair of grips and possibly an allen key to change the radiator tails.

Firstly, you will need to completely drain the system of all the water, then remove the caps to give yourself more room and then supporting the valve with a pair of grips to avoid damaging the pipework. Next, loosen both nuts with a suitable spanner. Make sure you use a cloth or towel underneath the radiator as although you have drained the radiator, there will be some drips that will run out.

Changing the radiator tails

Sometimes you need to change the radiator tails to match the new valves and you will probably need to use an allen key to unscrew them.

When fitting the new tails, be sure to wrap the threads with PTFE tape as this will stop any leaks. Refit the new tails by hand first and then and ideally finish off with a suitable ring spanner as the corners are easily rounded if you are not careful. Before fitting the new valve, make sure you put some mortar jointing compound onto the old and new joints.

It may be necessary to lift the radiator slightly on it’s brackets to get the new valve in. Screw the nuts on by hand first and when finally finishing off with the spanner, support the valve again with the grips to avoid damage to the pipework. With the new valve fitted, the system needs to be refilled and also bled.

One radiator should be TRV-free

Please note that one radiator in your house should not have a thermostatic valve fitted to it. The most common place to have a radiator with a non-thermostatic valve is in the bathroom (or the room where the thermostat is fitted). If all the other radiators are turned off then having at least 1 open allows water to flow through.

This can potentially stop any damage from occurring to your boiler or pump.

Energy regulations & notification requirements

As a commitment to energy efficiency, the government introduced a series of new building regulations in 2006 and these are worth bearing in mind when you think about installing thermostatic radiator valves. The contractor you get in to do the work must have a qualification in energy efficiency and upon completion of the work, they must fill out the correct notification forms to ensure they are in compliance with the building regulations.

For more information on this issue, please check with your contractor.