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.

The top (plastic) part of the valve is held on to the pipe by a large-ish ring.

  1. Turn the valve to the open (hottest) position.
  2. Locate the ring and unscrew it. (Turn it anticlockwise if looking from above.) If you cannot unscrew the ring by hand you will need something to grip it, such as a wrench, adjustable spanner, pliers or even a cloth – it’s a bit like opening a jam jar.
  3. Lift the top of the valve, complete with ring, away from 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 normally be about 4mm long, as in the 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 (not too tightly!), leaving the temperature 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 may need to be replaced by a plumber.

Extra Tip

A valve can become stuck closed when is left in the ‘off’ position 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.