Radiator valve head operation

[AnthonyL]

A question about the central pin in the thermostatic head of for instance

One of my radiators is not coming on. I've taken the head off and if I rotate the top part (ie hot to cold) the central assembly doesn't move though I can push it in with a screwdriver and it springs back but seems to require more pressure than I'd expect the little pin in the radiator valve could exert.

I've tried a working head from another radiator and the pin retracts as I go to 5 and protrudes as I go to 0.

So how should it operate and if faulty should the item referred to fix it?

The pins in both radiators are free and can be pushed down (= off?)

[Tim+]

Although the pins move up and down I think sometimes the sealing washer sticks to the seat.

A sharp rap to the side of the valve body with a small hammer can sometimes shock the jumper off its seat but this is only a temporary repair once its started sticking in my experience.

Tim

[Heliotrope Smith.]

Have you checked that the lock shield valve on the opposite end is in the on position?

[AnthonyL]

It's the valve head. Take it off and the radiator works. As in my OP I think the central column is not moving as it should.

[alan_m]

What is the ambient temperature of the room or within the TRV haed when in your hand whilst testing it? If its close to 29C then the wax in the TRV head will have already expanded close to its maximum to shut off the valve. First mark the position of the mechanism and then put the TRV head in the fridge for 5 minutes before checking the position again.

There will be a lot of force pushing back when you try and compress the wax in the TRV head with your screwdriver if the wax has already expanded due to a temperature approaching 29C

When the valve head is reinstated it may only fully open the valve if the temperature is below 12C. Any temperature above this and the valve will already be closing down and at, say, 20C it may be 50% to 75% closed. If in this sate the radiator is not getting hot then the system may not be properly balanced. In my experience balancing the system in hot weather that have TRVs is difficult and if I do any work on my system during the summer I wait until a really cold spell to fine tune balancing.

It may be possible to fit the head scewed. On a similar head I've found that I have to push it down quite hard to properly seat the valve base before doing up the silver ring/screw.

[Brian Gaff]

Yes there are two radiators like this in a room we rent for the talking newspaper, in the main the one working one is sufficient, but occasionally in really arctic weather it would be nice to get one going. The building manage could not give a xxxx of course. Brian

[AnthonyL]

It's autumn. It's the UK. It's time for the CH to come not the AirCon :)

The central column in a working head moves up and down just fine.

[John]

alan_m [e-mail]> wrote in news:gv22lgFo4r5U1 @mid.individual.net:

Good point: On mine the head can only seat in 6 positions - some sort of hexagonal seating.

[AnthonyL]

I think the penny is dropping slowly. There are at least two types of valve head. One which is purely mechanical so the user has to turn the knob to allow more or less heat through the radiator. The other is thermostatic so it attempts to stop the room from getting warmer than it is set to. Is that right?

[The Natural Philosopher]

Yes. The latter is called a TRV, Thermostatic radiator valve. In general a wax cylinder exapands and pushes the pin to cut off the rad at a given point

[AnthonyL]

Thanks, on my non-working one the cylinder does not change position as I turn it. On a working one the cylinder does.

On the presumably non-thermostatic one the central pin is clearly on a thread and just goes up and down with the rotation of the head.

I've not been careful enough about which type to select and which ones are best installed in which rooms. With my new-found education I shall save vasts amount of energy and help save the planet.