On Tue, 31 May 2011 11:49:12 +0100
Davey wrote:

On Mon, 30 May 2011 14:02:43 +0000 (UTC)
Dean Heighington wrote:

Davey wrote:
On Sun, 29 May 2011 14:05:44 +0100

Interesting, and I have found the reference you quote. So that's
not it, then.
I'll work my way around the house, checking all the valves in the
same way. I wonder if there is a known problem with the sensor
heads, or if they are not very good even when new? All of mine
behave the same way, ie not very well at all.
Thanks.

Check to see if the ones you have can be fitted to either flow or
return and that they are on the flow side of the rads if not.


According to the arrows cast into the body, they are for either
direction.
When I was working in industry, in process plant commissioning,
control valves like these were always installed on the exit end of a
heat exchanger, thereby keeping the unit pressurised. Keeping the
pressure in the unit behind the valve also resulted in better flow
control, so your mention of fitting to the flow side is opposite to
my training.

All the valves here are indeed on the return side of the radiators,
where I would expect them to be.
--
Davey.