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Diagnosing & fixing radiator valves that simply don't behave...yourself!

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There are some common problems that are darned easy to sort yourself.

Thermostatic radiator valves are brilliant ways to control temperature in a room, but they aren't perfect and some problems can crop up.

Do you have a radiator valve that just won't obey orders? A valve where no matter what position you put it at, the radiator is either always hot or always cold?

If so, here are two very common causes and this blog shows you:

  • How to work out which of the two causes it is.

  • How easy it is to fix them yourself...and it is REALLY easy...and no plumber needed.

If you are uncertain how thermostatic radiator valves should be used to save you money, see my very practical guide here. They are widely misunderstood and actually can save around £200 for the average home if used the right way, while still keeping you comfortable in your home.


Cause 1 - the valve is stuck - this is the most common cause

This may sound intimidating, but it is a doddle to fix. You don't need a plumber, and there is no chance of getting water everywhere if you follow these steps.

As you will see, it takes just 1 minute 13 seconds to fix this problem if this...the length of the video below.

The steps you will see in the video are:

  • Removal of the body of the valve (the 'white blob').

  • Pushing the valve control pin in a few times to make sure it moves freely.

  • Putting the blob back on.

  • That's it.

Once you have freed the valve pin, it should then move in and out around 3mm or so as you can see in the video.

A little more info below the video to help with technique.

Valves tend to stick if they haven't been used for quite a while. They still probably have many years of life in them so there probably isn't any need to worry about replacing them.

Often the ring can be undone with your fingers as I show in the video. You need to make sure you turn it the right way!....turn it anti-clockwise as you face the end of the radiator.

If the ring is a little stubborn try a damp kitchen cloth wrapped around the ring to allow you to get better grip on it.

If it IS a little stiff it'll be like removing the lid on a new jar of jam....a little tight to begin with and then it'll rotate easily.

Most of the time the rings can be undone by hands alone, but if it is particularly stubborn, you might need to use pliers like the ones below.

These tools are cheap and widely available. Their official name is water pump pliers. The ones in the photo are from Screwfix and only cost £7. You can also buy them at any DIY store, or even sometimes shops like B&M, Home Bargains or even pound shops. DIY stalls in open traditional markets will also sell them.

Using these pliers, it shouldn't need much effort at all to turn the ring - do use them as gingerly as you can though.

If it proves to be stubborn and you don't have experience of using tools like this do seek someone with the right level of DIY experience to help. If you are too forceful you can stress the plumbing fittings or potentially damage the surrounding pipework.

Trivia for the curious: the way these valves and white blobs work and what actually happens when they go wrong:

  • At the other (internal) end of the pin is a small valve that opens and closes to allow water to flow through the radiator.

  • When the pin is pushed in, no water flows through the radiator. SO, if the pin is stuck 'in', then the water will be allowed to flow through the radiator to its hearts content.

  • If the pin is stuck in the 'out' position, then the valve will be permanently shut, and water cannot flow through the radiator.

  • Basically, the job of the white blob is to respond to the temperature in the room and push the pin in and out. Its mission is to open or close the valve the right amount to get the room warm enough.

  • When the room is warm enough, the white blob pushes the pin all the way in, the valve closes, and the radiator cools down.

  • If the temperature in the room then falls, the white blob will gradually let more hot water into the radiator to warm the room up again.

  • Simples.


Cause 2 - The actual thermostatic control valve body itself (the white blob!) has failed

They do fail occasionally with age.

There is a simple way to work out if it is the blob itself that has failed.

It is pretty likely you will have radiator in the house with the same type of white blob.

So, try swapping the two blobs so the one you suspect of being faulty is now on another radiator. Even if the blobs you have on the other radiators aren't identical, it is still very likely that you will be able to swap them.

If your white blob HAS failed, then it'll mean the radiator you have moved it to will also disobey!

The same video above shows you how easy it is to remove the white blob itself. Whenever you refit a blob or fit a new one, it is much easier to do it if you rotate it to position 5 (or higher if the numbering goes higher on yours).

When fitting a blob, make sure you fit it in a position that will mean you can easily see the numbers on it. The photo at the top of the pages shows what I mean.

If it IS the white blob at fault, most of them are universally interchangeable these days.

So, any new blob you buy should fit.

If you are unsure, visit a builder or plumber merchant and seek their advice on what you are buying to ensure you can get one that will definitely fit.

Thermostatic radiator valves are usually only around £10 to buy.


Electronic thermostatic radiator valves

If you want to really focus on saving energy there are increasing number of electronic thermostatic radiator valves. They allow you to have precise temperature control.

They have built in timers that you can set to have different temperatures for different times of the day, and many have Bluetooth. There are even wi-fi ones, but these are a little expensive at the moment.

Some even sense your presence in a room and react accordingly. Others can even sense a window being opened and turn the radiator down automatically.

This is one of the cheapest electronic ones on the market at around £15.

They are all battery powered using regular AA batteries typically, which last several months.

You don't need a plumber to fit these. They go directly onto the radiator and fit on exactly the same as the standard white blob.


Other problems that radiators can have

There are other potential causes of a radiator getting either

  • Not hot at all

  • Not as hot as other radiators, or

  • Simply not getting the room warm enough

I don't currently have time to provide detailed information on these causes but here are some of the headline reasons for these other problems:

  1. The valve at the OTHER end of the radiator (known as the lockshield valve) is closed or almost completely closed.

  2. Lots of air in the radiator.

  3. Sludge in the bottom of the radiator.

  4. The radiator is too small for the room.


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If you have any other suggestions for additions or changes to site content do please let me know. While I have made every effort to ensure that the information contained on this website is correct, I cannot take responsibility for errors or omissions.

All content on the site should be treated as information and not advice. You should take professional advice where appropriate to different site articles.


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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