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Radiator thermostats...

 
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sean
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Joined: 28 Oct 2004
Posts: 41915
Location: North Devon
PostPosted: Tue Sep 20, 05 1:36 pm    Post subject: Radiator thermostats...  Reply with quote    

Our central heating has thermostats on the radiators, which is good, but they're crap which is bad. Effectively the temp adjustment on them doesn't work so they're either on or off.
How difficult is it to change them, and has anyone any recommendations on makes/models?

Trev



Joined: 09 Sep 2005
Posts: 69
Location: Wokingham DC, Berkshire
PostPosted: Tue Sep 20, 05 2:15 pm    Post subject: Reply with quote    

Sadly I'm in the same predicament... I really don't see how they can work, they're placed right next to the heat source so how can they be set to the temperature of the room - this is probably why they don't put temperatures on the dial, just ambiguous numbers. I would be glad to hear of any alternate solution of suggested workaround for the products.

dougal



Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
PostPosted: Tue Sep 20, 05 3:06 pm    Post subject: Re: Radiator thermostats... Reply with quote    

sean wrote:
Our central heating has thermostats on the radiators, which is good, but they're crap which is bad. Effectively the temp adjustment on them doesn't work so they're either on or off.
How difficult is it to change them, and has anyone any recommendations on makes/models?


I'm assuming that they are reasonably recent devices.
In which case, they probably *do* work, just very s_l_o_w_l_y. They are very, very unresponsive, but they do work. And its very difficult to detect/monitor exactly what the valve is actually doing - the best you can do is check the radiator temperature - at the *outflow* (not the top!)

The idea is that they are a thermostat ie they maintain a static temperature in the room. They are *not* thermometers or "controllers" which might try and achieve a particular set temperature.
They are trying to maintain the head-level temperature (for comfort) by trying to keep the ankle-level temperature constant-ish. Which is dependent on the air movement in that room. (And different rooms have different vertical temperature gradients...)

They really are *not* items to be readjusted daily, after their initial setting.
I'd suggest that it'd be pretty difficult to find a reasonable set point at this time of year.
When it gets cool enough to need the heating on, you can tweak each one a little (10% of the range?) and then consider whether the room is too hot or cold - but only an hour or more after you tweaked it...
And once you have a happy medium - leave it alone! The idea is that *you* do *not* have to "turn it up a bit" on a cold day...
If the outflow temperature never varies, and is pretty cool, thats an indication that the lockshield (balance) valve is closed too much. In fact, with stats, the function of balancing is only to make the initial warming up process happen evenly (not to balance the steady-state heat around the house).


Thermostat detail points. Some can deal with water flowing one way only. Bi-directional ones give more mounting flexibility - IMHO its a good idea to mount the head horizontally, so its further away from the rad.
Its considered bad practice to have more than one thermostatic valve in the same room. It should be on the biggest radiator. (You can just set the t-valve on the others to maximum, no need to remove them.)
For the same size pipe, they should be fairly interchangeable, as far as size goes. It'll be a drain down job to change the valves, and you'd need to tighten the joints to prevent leakage on refilling the system. Non-trivial, but not highly skilled.

I don't think there's much difference between brands on their *control* capabilities. Some might say there were differences in *durability* (they used to have a terrible reputation for sticking - original Danfoss ones particularly.) And they are pretty cheap.
There are odd *electrical* (rather than pure mechanical expansion/contraction) controls, which can have a remote room temperature controller, or even be remotely computer controlled and monitored, , but these are naturally *very* much more expensive...

wellington womble



Joined: 08 Nov 2004
Posts: 14967
Location: East Midlands
PostPosted: Tue Sep 20, 05 5:06 pm    Post subject: Reply with quote    

So they can't mantain different heating 'zones' in a house, then? We have difficutly, as we have a loft conversion, which is still cold, when the rest of house is far too warm, and if we put the thermostat up there (its a remote one) its warm enough, when everywhere else is far too hot, and the heating is still on when the woodburner is doing it job! As I only really want a warm bedroom in the morning, we are using a heated towel rail, on a timer plug at the moment, but himself is talking about a two zone system to maintain the temperature with two thermostats, - one for the bedroom and one for the rest of the house - would thermostatic rad valves work instead?

dougal



Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
PostPosted: Tue Sep 20, 05 7:59 pm    Post subject: Reply with quote    

wellington womble wrote:
So they can't mantain different heating 'zones' in a house, then?
Yes they can, if the doors are closed! That's why they are effectively required by the current regs.
Quote:
We have difficutly, as we have a loft conversion, which is still cold, when the rest of house is far too warm, and if we put the thermostat up there (its a remote one) its warm enough, when everywhere else is far too hot,
Room stats are a different matter to rad stats...
It sounds like your loft conversion needs a bigger radiator and/or better insulation! (Maybe only the lockshield valve opened a bit, - or others closed down a bit)

I didn't mention that you can muck up the control scheme by having a room stat in a room with a rad stat...

As you have discovered, once the room-stat-room is hot enough, heat is switched *off* for the whole house...

Wireless room stats are very kewl, but they are better seen as avoiding difficult/unsightly wires, rather than portable comfort control...!!!

Quote:
As I only really want a warm bedroom in the morning, ... himself is talking about a two zone system to maintain the temperature with two thermostats, - one for the bedroom and one for the rest of the house - would thermostatic rad valves work instead?

If you have the potential to install zoned pipework, that would clearly be a better solution - you could, with a second timer, avoid heating the bedroom(s) during daytime, even if you are at home... however, rad stats in the bedrooms would provide individual room temperature moderation - probably better than a bedroom room stat.
I'd expect (dunno what you've got) that the easy way to do it would be to use a motorised valve to switch off the bedrooms (ie don't bother arranging it so the bedrooms could be heated without heating the living rooms.)

Treacodactyl
Downsizer Moderator


Joined: 28 Oct 2004
Posts: 25697
Location: Jumping on the bandwagon of opportunism
PostPosted: Tue Sep 20, 05 9:06 pm    Post subject: Re: Radiator thermostats... Reply with quote    

dougal wrote:
I don't think there's much difference between brands on their *control* capabilities. Some might say there were differences in *durability* (they used to have a terrible reputation for sticking - original Danfoss ones particularly.) And they are pretty cheap.


I would say that some brands are better and many are useless. Someone who trains gas fitters basically said most are rubbish. I cannot remember the brand they recommended but the average priced ones I bought about 4 years ago stuck from the first winter and when I bumped into the manufacturers at a building show they weren't surprised.

Most people in houses I've seen with TRVs fitted tend to either set them full on or full off so I would question why the new building regs insist on them.

One thing to remember is that on most systems they should *not* be fitted to all rads. At least one rad should be free to stop the heating from overheating.

Trev



Joined: 09 Sep 2005
Posts: 69
Location: Wokingham DC, Berkshire
PostPosted: Wed Sep 21, 05 11:00 am    Post subject: Reply with quote    

dougal, thanks for that - was having a major thickness attack there - I concur with your mounting away from the radiator opinion. You mention:

Quote:
Some can deal with water flowing one way only. Bi-directional ones give more mounting flexibility


is one limited to placing the valve on the inflow side of a radiator? My thought is that, since the outflow pipe will naturally be closer to the ambient temperature than the inflow pipe, is there a possibility to place the "TRV" on the outflow pipe or am I spouting a load of ?

dougal



Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
PostPosted: Wed Sep 21, 05 11:15 am    Post subject: Reply with quote    

These Honeywell items, for example, are specifically mountable horizontally or vertically, on inlet or outlet.
http://www.discountedheating.co.uk/shop/acatalog/Online_Catalogue_Honeywell_267.html

Guest






PostPosted: Wed Sep 21, 05 9:13 pm    Post subject: Reply with quote    

My parents system dates from the 1970s and the thermostats work on their radiators. I should ask for your monety back if they can't fix it easily.

Jonnyboy



Joined: 29 Oct 2004
Posts: 23924
Location: under some rain.
PostPosted: Wed Oct 05, 05 2:40 pm    Post subject: Reply with quote    

Got my system up and running yesterday. the thermostats work on the room temperature according to my plumber, and when I altered one it had cooled the radiator noticably within 30 mins ( I wasn't checking it often)

Northern_Lad



Joined: 13 Dec 2004
Posts: 14210
Location: Somewhere
PostPosted: Wed Oct 05, 05 2:59 pm    Post subject: Reply with quote    

I've got them on all my radiators, and so have my parents.

Asside from a couple of mine whistling while closing (not been tightened since they were installed) they're great.

They can open and close themselves depending on the temperature and setting.
They can work as most heat is generated by the top of the radiator.
The do maintain different temperatures in different rooms. (I know this as my room used to be much cooler than the rest of the house when I lived with parents)

Should be a breeze to change.

Drain the system or, if you're lucky, isolate and drain the radiator in question).
Remove the old valve (should be two nuts)
Attach the new valve.
Refill radiator/system.
Bleed.

Treacodactyl
Downsizer Moderator


Joined: 28 Oct 2004
Posts: 25697
Location: Jumping on the bandwagon of opportunism
PostPosted: Wed Oct 05, 05 7:04 pm    Post subject: Reply with quote    

Northern_Lad wrote:
Should be a breeze to change.

Drain the system or, if you're lucky, isolate and drain the radiator in question).
Remove the old valve (should be two nuts)
Attach the new valve.
Refill radiator/system.
Bleed.




Ensure the sludge from the old rad doesn't stain the carpet.
Ensure enough PTFE tape, or whatever you use, is used to provide a good seal.
If refilling whole system ensure you have inhibitor/antifreeze in the system.
Bleed, bleed again, and carry on bleeding.

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