radiator valves explained

Radiator Valves Explained: How They Actually Work

Last updated on February 22nd, 2024

Radiator valves allow you to turn off, control the temperature in a room, and balance radiators.

Whether it’s because the radiator is not getting used or you want to remove a radiator for decorating, closing the radiator valves will isolate the radiator from the central heating system.

I have been working on central heating systems full-time for over a decade.

Types of Radiator Valve

All panel radiators, designer radiators, cast iron radiators, and towel radiators should have two radiator valves on each radiator.

There are only really two different types of radiator valves, thermostatic radiator valves (TRVs), and lockshield valves.

All other types of radiator valves can fall into these two categories:

  • Manual radiator valve: Lockshield valve with a head on to turn with your hand.
  • Twin entry radiator valve: Lockshield valve which connects both pipes for the radiator to go on one side of the radiator.
  • Straight radiator valve: Straight radiator valves can be lockshields or TRVs and are normally used on the bottom of towel rails, so the pipes can go straight down from the radiator to the floor.
  • Angled radiator valve: Lockshield and TRVs are angled on most radiators. They go on the sides of the radiator and angle the pipes down to the floor.
  • Corner radiator valve: Corner radiator valves are normally lockshield valves and are used to take the pipes from the radiator straight back to the wall behind the radiator.
  • Radiator Bleed Valve: Not really a valve but they do get called this. There are different types of radiator bleed valves and they are for bleeding radiators.

How Does a Radiator Valve Work?

A radiator valve works like a tap on a central heating system.

It lets the hot water in the system flow through the radiators to heat the room when it’s open and isolates the radiator from the system when they are closed.

When a radiator valve is turned clockwise, it screws the spindle down over the pipe end of the valve until the back seating surface is pressed down, which stops the water from flowing into the radiator.

A radiator valve is often the cause of a radiator not heating up by becoming blocked or broken.

How Does a Thermostatic Radiator Valve Work?

A thermostatic radiator valve works by feeling the temperature in the room, like a room thermostat.

When the room reaches the temperature (setting) you have it set to, the valve will close and turn the radiator off until the temperature of that room has dropped.

Thermostatic radiator valves use wax, liquid, or gas-filled capsules that contract and expand to move the insert to open and close the valve accordingly.

thermostatic radiator valve
Thermostatic radiator valve

How to Open a Radiator Valve

To open a radiator valve, you need to turn it anti-clockwise as far as it will turn. Some radiator valves can be turned with your hand, but for some, you will need to use a tool.

To open a thermostatic radiator valve, you turn it anti-clockwise until it’s on the setting you want it on, or turn it as far it will go to leave it open fully at all times.

How to Close Radiator Valve

To close a radiator valve, you need to turn it clockwise as far as it will turn.

To close a thermostatic radiator valve, you turn it clockwise until it’s on zero.

If a closed radiator valve does not stop the heat to the radiator, then the valve is not closing properly, and you will probably need to replace the radiator valve.

Some radiator valves do not get opened or closed for years, which can cause them to leak when closing for the first time.

You will either have to fix the leaking radiator valve or replace it.

Radiator Valve Tools

Some radiator valves can be turned on and turned off with your hands, but some need tools.

Radiator Allen Key

A radiator Allen key (or hex key) is a large key used for fitting and removing certain types of radiator valve tails.

There are also Allen keys for opening and closing certain radiator lockshield valves. Danfoss lockshield valves need a 6mm Allen key.

Lockshield Valve Key

A lockshield valve key is a spanner-type tool to open and close lockshield radiator valves. They turn the spindle on the valve, but the spindle tops come in all shapes and sizes.

There are different types of lockshield valve keys, some with one single key, some with 3, 4 or more.

I normally use water pump pliers as I always have a pair on me when I’m at work, and they can be used for most different lockshield valves.


Radiator valves are needed to control the flow of water (heat) through radiators and can be used for fixing radiator leaks, balancing heating systems, and many other uses.

Feel free to ask me any questions in the comment section below and I’ll try my best to help.

Please share this post if you find it helpful.


What are the two valves on a radiator for?

The two valves on a radiator are for controlling the temperature of the radiator (and room), balancing radiators, and for isolating a radiator from the heating system.

What side of the radiator is the lockshield valve?

The lockshield valve can be on either side of the radiator. They are normally fitted on whichever side is best for that particular room.

For example, when I’m fitting a new radiator, I will usually fit the thermostatic radiator valve on the side which is the furthest away from the door. This is so it’s less affected by the temperature outside the room, and the lockshield will be fitted on the other side.

Should lockshield valve be fully open?

For most radiators, the lockshield valve should be fully open. When balancing radiators, the lockshield valve on some radiators will be partially closed to spread out the heat to other radiators that are not getting hot enough.

Are radiator valves open or closed?

Both radiator valves need to be open for the radiator to get hot. If any radiator valves are closed, the radiator will not get any heat.

A radiator valve needs to be turned anti-clockwise to open.

What is the best way to use a thermostatic radiator valve?

The best way to use a thermostatic radiator valve is to set it to the correct temperature you want the room to be.

You will have to check with each manufacturer for the temperature, but the number 3 setting on a TRV is usually around 20 degrees Celsius.

If you don’t use a certain room in your home, the best way to use that thermostatic radiator valve might be to turn it off or on to the frost setting. This means the radiator will only come on when that room is freezing cold, normally 7 degrees Celsius.


  • Steven Reid

    I am a full-time plumber and Gas Safe registered engineer. I incorporated Housewarm Ltd. in 2011 to provide heating and plumbing services to homes in Newcastle upon Tyne, England. I now blog about what I've learned over the years to help DIYers and plumbers.

    View all posts
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