Can't shut off radiator manually with TRV

[Drake]

In a domesting hot-water CH system, What would cause a TRV to fail to shut the radiator off when it is tightened down fully?

Thanks,

Drake

[Andy Hall]

In normal operation it would either be crud or corrosion around the valve seat or that the head has failed.

If your problem is that you want to shut off the valve to be able to remove the radiator, then valves normally come with an extra plastic cap that is screwed on in place of the head for this purpose.

[Fash]

Lots of TRVs don't claim the ability to completely shut off flow. Some have a positive 'off' position but usually make some claim to this as an added feature in the blurb. Therefore you may be wrong to call it a 'failure'. If this is the case, you better hope you haven't upset it too much by cursing it and otherwise saying rude things about/to it!

Fash

[Drake]

Thanks for the reply (Likewise to Andy). The odd thing is that the TRV doesn't even seem to be controlling the temperature of the rad at all. It seems to be permanently on 'very hot'. Seems to defy logic...

Drake

[Dave Plowman (News)]

Have you checked the valve pin is free to move?

[Dave Baker]

Not if the head part has been assembled wrongly. In fact logic points to this as being the main possibility. Take the head of the TRV right off the rad by unscrewing the locking nut at its base. You should see the spring loaded pin sticking out of the base on the rad which has the shut off washer on its other end. Push it down fully and see if it springs back up freely. If so the shut off valve part is ok.

Now check the head of the TRV. It should be in two main parts. The bottom bit which screws to the base on the rad and the top bit which rotates and contains a plunger which expands as it gets hot to control the position of the shut off pin. Remove any grub screws and take the two apart. You'll see splines or buttresses inside both which determine how much the top bit can rotate relative to the bottom bit and therefore how far down the plunger can be screwed. Depending on how the two are oriented when you start to screw them together you'll get more travel or less travel. Yours may differ slightly from this description depending on its make but if you play with it a while you'll see how it works.

Sounds like someone with itchy fingers has had yours apart and not put it back together properly so the plunger never screws down far enough to close the shut off pin. The rest you should now be able to work out for yourself, perhaps with a little trial and error.

-- Dave Baker Puma Race Engines

Camp American engineer minces about for high performance specialist (4,4,7)

[Dysanovic]

I am about to remove a radiator which has a TRV valve. FYI the TRV valv

I had was a Drayton/Invensys model, and it was not obvious how to g about completely closing it.

I thought I'd need a safety cap as the TRV only apeared to have a fros setting. What I found is that with a little bit of force the TRV coul be turned to the '0'/decorators setting (i.e. positive 'off' position) but the instructions did not state this!

If it is permanently hot it I think it could be due to the fact tha the radiator is not correctly balanaced. I believe you balance th radiator by altering the lock shield valve (but don't quote me o that!).

Drake Wrote:

-- Dysanovic