One radiator is cold when the rest are hot


The heating is working properly, but a radiator does not heat, even if the thermostatic valve is turned right up.

Likely Cause

Part of the the valve is stuck closed.

What you can do

It is worth trying to free the stuck valve yourself if you have a wrench, or a tool like that, which will grip the ring under the plastic part of the valve – the ring holds the top of the valve onto the pipe.

  1. Turn the valve to the open (hottest) position.
  2. Locate the ring and grip it with the wrench. Unscrew the ring anticlockwise (if looking from above).  Occasionally, it is possible to turn the ring by hand.
  3. Lift the top of the valve, complete with ring, off the top of the pipe.
  4. You will see a small pin coming through a hole in the pipe top. If you can only see the top of the pin as a small bump, this is the problem – it should be about 4mm long. See photo below.
  5. Press, or gently tap, the top of the pin. If you are successful in unsticking the pin, you will see it rise as the water in the pipe pushes it upwards.
  6. Now the pin is up, screw the top of the valve back on, leaving the setting to high.

TRV with top removed

The radiator should get hot and, with luck, the valve will now work normally. Sometimes you have to repeat this a few times. If the valve still does not function after that, it will need to be replaced.

Extra Tip

A valve can become stuck closed when is left in the ‘off’ posistion for a long time. If the heating is to be left off over the summer, for example, it is worth leaving all the valves in the middle position to prevent this happening.

If this does not work

Call a professional plumber. The valve may need changing.