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Category: Plumbing

At this time of year, this is a common question that comes into us here at DIY Doctor. Our heating in just going on after a long hot(?!) summer and this is when many of the problems occur. If one of your radiators fails to get hot when all the others seem to be working fine, then suspicions are immediately raised about the TRV or Thermostatic Radiator Valve. Often with good cause; work through our quick trouble shooting guide below to see if you can find problem.

What is a TRV?

A TRV or Thermostatic Radiator Valve is one of the valves that is fitted to your radiator. It is easy to spot as it is the one you can turn to set the temperature that it will open and then turn the radiator on. The one at the other end is call a lockshield valve.

TRV or thermostatic radiator valve

TRV or thermostatic radiator valve

A modern TRV or Thermostatic Radiator Valve – this controls the temperature at which the radiator will come on.

The TRV has a thermostat which responds to the room temperature to open or close the valve. This is why if only one of the radiators is not working it is thought to be one of the most likely causes.

While this is often the case, it is still sensible to work through a methodical fault finding process to ensure that you find the true cause of the problem.

Quick Checks to Find Out Why One Radiator is Not Working

Here is a quick guide to the things that you should check if you discover that one of your radiators is not working, not getting hot, when all the others are working fine.

  • Have you bled the radiator? See our project about how to bleed radiators here
  • Check that the TRV is on – not set to zero or to the frost setting (typically a snow flake icon); if the room is warm enough already the valve might be correctly switched off (for the temperature setting)
  • Temperature settings on TRV valve

    Temperature settings on TRV valve

  • Good airflow – The TRV responds to the room temperature, but if it is in a radiator cabinet or the radiator is behind curtains or furniture it could be ‘sensing’ that the room is too hot and closing the valve. Make sure there is good air flow
  • Is the TRV working? There are two things that you can quickly check on the suspect TRV
    • Check the piston or plunger can move to open and close the valve – you will have to remove the thermostat unit to do this by unscrewing the hand turn-able thermostat removal nut
    • Check the thermostat is working – the easiest way to do this is to swap it with another radiator and see if it works
  • Is the Lockshield Valve open enough – this is the valve at the other end of the radiator. This needs to be open for the radiator to work
  • Lockshield valve

    Lockshield valve

  • Blockage or Airlock – at this stage you can be fairly confident that you have ruled out everything else and it is either a blockage or airlock. You will now have to consider draining the radiator to clear the obstruction. Find out more about draining radiators on the link above

Get that Radiator Working Again!

Hopefully this will have solved the problem, and in many cases the causes of a single radiator not getting hot will have been cured by a little care and maintenance on the TRV.

Love them or hate them they are here to stay, so you might as well get on top of your TRV maintenance because you know that they will always break at the more inconvenience time!

Have a look at our project on TRV’s for a full explanation on how to work through a methodical fault finding process in full. We also cover essential TRV maintenance and how to remove a TRV if you have to.


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