Thermostatic Valves problem

A while ago, I fitted thermostatic valves to all the radiators in my house. All the radiators work ok (in that they switch on and off ok - They vary in degree of warmth, but thats another problem ) except for one.

The radiator in the spare room will NOT turn off, even when I remove the thermostat part and put on the manual cap.

When I fitted these, I simply replaced the existing valves - is it possible that I've fitted the thrermostatic valve to the wrong end of the radiator, and if so, how would I determine which is the right end in future?

Is it more likely just to be a dodgy valve?

Any suggestions would be VERY appreciated. Thanks in advance.

I know the old type of valve (20 years ago) had to be fitted on the flow side of the radiator, ie the side that warms up first, but i thought modern valves could be fitted on either side; it might be worth checking the instructions.

Also with the old Drayton valves the needle protruding out the top of the valve body used to get stuck, and used to have to free it by depressing the needle a couple of times.If it was stuck, it would be either ON or OFF alll the time.

Thanks for the reply, appreciate your comments.

I've now bought a new valve, instructions here.

I'm still none the wiser. On one hand the instructions say that 'either head orientation can be achieved on both the flow or return of the radiatior' but on the other 'valves should be mounted vertically on the flow, horizontally on the return'. Isn't this contradictory?

It goes on to say that 'the valve can be fitted on the flow or on the return; The direction of flow arrow must be observed'. I assume this is referring to a direction of flow indication on the valve; a small arrow above the lower compression joint as shown in this picture?

Ok. but how do I determine the which is the flow and which is the return of my radiator? FYI, the radiator IS NOT yet plummed in.

I'd be grateful if someone could point me in the right direction.

sounds like the stat that wont shut off is faulty or very unlucky with a one pipe system thats getting condution up the pipe .Looks like thats an old style westherm valve. The arrow on the side of the valve ? has it got 2 arrow heads at a 90 degree angle or just 1.

Can't see it saying 'valves should be mounted vertically on the flow, horizontally on the return' anywhere.

Anyway, respect the arrows on the valve. Before you plumb it in you'll have to find which pipe is which. Put the ch on and the flow gets hot first!

Can't see it saying 'valves should be mounted vertically on the flow, horizontally on the return' anywhere.

Click to expand...

After 'correct installation', third row down.

Thanks all for your replies. I should be able to manage now.