Hi all,

.... Following on from my first enquiry / thinking out loud / trying to
help an elderly neighbour get some control over her central heating
....

I've previously swapped her Potterton Netaheat Electronic (10-16?)
control board, more recently the pump and today looked closer at her
TRVs with the thought to adding a room stat as she said 'none of the
TRVs work and haven't from new ...'.

So, looking today, most of the TRVs are 'Temtrol' units that I believe
we

"The valves were made by a Swedish company. They were originally sold
under the Honeywell brand from 1974 to 1980; then under the Temtrol
brand in the UK by Harvey Habridge Ltd."

http://community.screwfix.com/message/1190124#1190124

Also:
"Comap Westherm 5 heads fit these valves."?

Anyway, they look like this:

https://dl.dropboxusercontent.com/u/...%20TRV%201.jpg

I took the head off of one of them and tested the action of the valve
and it seemed to move freely against a moderate spring. However, the
amount of travel was only a couple of mm? I tried another with similar
results.

https://dl.dropboxusercontent.com/u/...%20TRV%202.jpg
(The brass collar goes up under the head and onto the top of the valve
body and the plastic pin pushes down to actuate the valve).

So, I removed the stop pins ...

https://dl.dropboxusercontent.com/u/...%20TRV%203.jpg

.... and tightened them all down to a mild finger tight and then fired
up the system and it seems they *can* actually shut off the water
flow. ;-)

Then, whilst watching the IR thermometer on the rad flow I slowly
eased each TRV open until I saw the temperature increase indicating
the valve about to open and left it there (the air temp was about 20
DegC at the time).

There were two new rads that had more modern TRVs:

Bathroom:
https://dl.dropboxusercontent.com/u/...ldog%20TRV.jpg
Hall:
https://dl.dropboxusercontent.com/u/...ther%20TRV.jpg

We will need to run the system up on a cold day to know how well it
all works and then probably tweak from there.

FWIW, I brought one of the Temtrol heads home and put it upside down
in a frying pan with a little bit of water. I balanced a wooden
spatula between the stat rod and the edge of the frying pan and had
the handle up against a rule, held vertically (It was balanced to give
me a x2 reading as it was easier to measure). ;-)

Very rough final figures (DegC / mm)

16 / 0
35 / .5
40 / 1
65 / 1.5
85 / 2

Now, over that temperature range I would imagine it would operate the
actual valve over it's full range but even a small movement (say 1mm)
felt like it might make a big difference to the temperature (heating)
of the rad(s)? Not sure how much heat is conducted to the stat from
the plumbing or radiated from the rad itself though (ie, would the
stat ever see those temperatures if the CH water was running at 60 and
the room was 20 DegC)?

Now, I understand that new valves might offer more range and / or be
more predictable but 1) I'm not sure what the chances are they would
be a straight swap for these older units (specifically feed pipe
alignment etc) and 2) I'd have to drain the system to fit them (and
all the worms that might reveal (summer job)).

Lastly, reading the user instructions for the little Honeywell time
switch it suggests that it has a rechargeable battery that 'should
last one week'. It would seem that it doesn't recharge any more and I
wondered if they were (d-i-y / technical) 'user replaceable'?

Could it be one of these:
http://cpc.farnell.com/1/1/54303-bat...50h-varta.html


I think it could be a ST699 as it looks like a 24 hour version?
https://dl.dropboxusercontent.com/u/...timeswitch.jpg
(crap picture)

I've not tried yet but can you easily remove the timer from it's
backbox without it falling apart or its tabs breaking off etc please
(I was thinking 'old plastic' here)?

Cheers, T i m

p.s. Google threw up that I'd asked a similar TRV questions in 2008
but her husband died soon after and hence nothing was done about any
of it (till now).