Was: Old CH, new (wireless?) stat? Now: TRVs and timer battery.

[T i m]

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 were:

"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."

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

Anyway, they look like this:

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.

(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 ...

... 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:

Hall:

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:

I think it could be a ST699 as it looks like a 24 hour version?

(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).

[harryagain]

There's no point in getting your knickers in a twist over TRVs. They work very poorly as they are influenced more by the radiator temperature than the room temperature. Unless you get ones with remote sensors.

>

[T i m]

Thanks for that. I had actually meant to ask that in my last post.

So, would they (when working at their best etc) not give enough control to manage the temperature in a bedroom etc? Keeping it off being cold and not letting it get too hot?

If not, why do so many people seem to have them fitted these days (the direct ones even, I can see how 'remote' versions could be more accurate)?

Cheers, T i m

[news]

They can certainly be very successful in this application (mine certainly are). Keep the bedroom door closed and the TRV can establish a temperature that is significantly different to the landing. They "might" not be so successful at keeping lounge temps within +/- 1 or 2 degs.

[T i m]

I'm guessing age / quality might come into this a bit as well?

Ok, thanks.

Understood, so, (recapping something someone suggested previously) we might be able to say set the bedroom TRVs to 'cool', the lounge TRV to hot but with a lower flow rate (to ensure 'upstairs' got warm 'enough' and via the isolator valve?) and then use a room stat to manage the lounge?

Cheers, T i m

[news]

Well quite possibly, mine are all Drayton and

I would say that should be very achievable.

[T i m]

Agreed ... and I'm waiting for a cold day to test the process from scratch. ;-)

Understood. They are currently left with the knobs free to rotate and so I can set them to whatever temperature is required (with the scope of these old TRVs etc). One set I can re-insert the pins, hopefully allowing the temperature range of 'frost protection' to 'warm enough'. ;-)

Great, thanks. ;-)

Cheers, T i m