Which is the best place to put a TRV on a radiator


I am upgrading my radiators which have been in the house since the 70's. My question is the TRV spec states it can be used on any input or output of the radiator in either horizontal or vertical mounting!
OK this is great but which setup is best or does it just not matter?
My other question is if I put TRV's on all the new radiators in the house what should be done with the main electronic thermostat which controls the heating pump, as if all the TRV get to there set temperatures and shut off the water flow the heating pump will have no ware to pump to!
Spec given: Honeywell Radplan 120 Angled Radiator Valve 15mm Provides individual room temperature control by varying the flow of water through the radiator. Approved to EN 215. Bi-Directional Flow Valve Body Wax Sensor for Consistent Performance Matching Lockshield Horizontal or Vertical Mounting
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Firstly.. I am not a plumber, but as I understand things you need to leave one rad without a TRV on it, so that the water still has somewhere to flow should all the other TRV's be 'off', unless your system has some form of flow bypass thing.
As I said I'm not expert!

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aye, we've just had a complete new system fitted with no previous system fitted & the one in the hall down downstairs has no trv fitted, where as all the others in the house ( 8 ) have trv's fitted.
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That make good sense.
So do you have a main electronic wall thermostat for the pump?
If you do is it in the hall with the radiator without the TRV?
If you don't does the pump run all the time when the heating is on. What stops the hall getting to hot?
Jon
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yes, its a wireless one, very clever didnt know you could get such things for heating.

yes, its in the hall.
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We've recently had our CH re-done, including 2 of these wireless thingies (for 2 zones - upstairs and down). A good tip from the installer was to avoid fixing the stats anywhere permanently until we've been through a winter and experimented with different positions (e.g. close to rad, close to front door, higher up or lower down etc.)
It'll be inetresting to see if we can find the optimum positions - but given the basic dilemma of wanting to demand heat, without over-heating hall areas, I'm not over confident.
The other thing which intrigues me, is that not putting TRVs on hall rads is fine - but shouldn't both valves therefore have lockshields - else someone may decide to shut the rad off completely.
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Martin
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Correct, lockshield valves with the head removed.
Aam
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The whole point of a main thermostat is to create a boiler interlock. If you only use TRVs then the water in the system is controlled by the boilers thermostat not by external temperatures. It is usual for the stat to be in a hallway with a rad that has no TRV. Part L of the building regs apply to new CH installs and would not allow only TRVs.
Adam
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Thanks for that. I will move the main thermostat to the hall. Should be easy as it's only the other side of the wall from the front room, so I can drill a hole thought the wall and extend the wire.
I take it the theory is the hall is the coldest place in the house and therefore the last place to warm up?
I was thinking it would be better if the pump was like a power shower pump and did not pump if all the TRV were closed, that way all the rooms would be more independent, as the above way the heating stops when the main thermostat is up to temp!
Jon
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And partly because the hall is a communal room with no secondary heat source such as fires and cookers. A room full of people watching TV can affect the temp in a well insulated room.

If you want to run lots of wires it can be done!
Adam
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Immediately prior to last Winter I installed TRVs on all my radiators bar the hall rad. I have a digital room thermostat in the hall.
I can understand your confusion about this - I felt the same at the time. What is to stop the hall over-heating very rapidly and then switching off the pump before the rooms controlled by the TRVs reach temperature? In practice this has not happened. I do, however, set the room thermostat to a slightly higher setting that I did prior to installing the TRV's. This has ensured that the rooms controlled by the TRV's can reach temperature without interference!
With regards to actual installation of TRV's - I also fitted a type which could be installed on either inflow or outflow of radiator - and either horizontal or vertical.
I installed all my TRVs in a horizontal position because I felt that put the 'capsule' further away from the radiated heat output from the rad. This should mean that the TRV will be more likely to respond to actual room temperature - rather than radiator temperature (which will not be the same of course).
With regards to which end of the rad to fit the TRV - I simply worked on the principle of which end was easiest to reach for adjustment!
I have had no problems since the installation and certainly all rooms tend to maintain a more steady temperature now. Before fitting the TRV's it seemed we were always adjusting the room thermostat because the living room became either too hot or too cold. This no longer happens!
Kev
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OK on your advice it all makes good sense.
What temperature do you set your digital room thermostat in the hall to?
I was also thing the TRVs would be best in horizontal position, but was concerned as I have not noticed TRV being installed this way very often. Perhaps this is because the TRV would be more prone to damage as it sticks out more.
I was also thinking the TRV would be better on the output (return flow) of the radiator as the water should be cooler and not effect the TRV as much.
Jon
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22 deg C.

I suppose this could be a problem in some situations - although has not proven to be in my home. One advantage of positioning the TRV's horizontally is that it is easier to 'read' the temperature setting. You can place the adjuster so that the 'reading' point faces upwards and you just have to look down to read the number. With the TRV vertically you would have to crouch down and look sideways to see what the number is. Hardly a major issue because once properly set they should not require regular adjusting!

A valid point - although personally I would place ease of access as a higher priority.
Kev
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the flow in the hall radiator with the lockshield valve you can control the rate of temperature rise in the hall and balance it against the heat rate rise in other rooms. It should be adjusted so that the hall is marginally the slowest area to come to temperature with openings to cooler areas controlled so that the hall is the first (again marginally) to lose heat and create boiler demand.
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.. >> .. >>Immediately prior to last Winter I installed TRVs on all my radiators bar .. >>the hall rad. I have a digital room thermostat in the hall. .. >> .. >>I can understand your confusion about this - I felt the same at the time. .. >>What is to stop the hall over-heating very rapidly and then switching off .. >>the pump before the rooms controlled by the TRVs reach temperature? In .. >>practice this has not happened. I do, however, set the room thermostat to a .. >>slightly higher setting that I did prior to installing the TRV's. This has .. >>ensured that the rooms controlled by the TRV's can reach temperature without .. >>interference! .. >> .. >You shouldn't need to run the hall at a higher temperature, if you throttle .. >the flow in the hall radiator with the lockshield valve you can control the .. >rate of temperature rise in the hall and balance it against the heat rate rise .. >in other rooms. It should be adjusted so that the hall is marginally the .. >slowest area to come to temperature with openings to cooler areas .. >controlled so that the hall is the first (again marginally) to lose heat and .. >create boiler demand.
I am still a bit confused ... just moved to a "new" house.
Rads have TRV's ..... There is a wall thermostat in the hall at bottom of the stairs ... and NO radiator.
So ......... if I set the hall thermostat to 20deg and wish the other rooms to be the same temperature (20 deg) with doors shut, I can control rooms with TRV's .... right ?
So what happens when the rooms reach 20deg? I assume the TRV's shut the water feed to the rads.
So what is happening in the hall and the upstairs landing space etc ? Hot air rises so will the boiler keep grinding away until it is 20deg at the bottom of the stairs in the hall to the top ?
I do not really want it that warm up there.
Mike P
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reaches temperature last and removes demand from the boiler. That way you can guarantee that all rooms controlled by TRVs will have reached their individual demand temperatures by the time the electrical thermostat shuts down the boiler. As you say, the TRVs will stop the other room temperatures rising much above their set temperature.
Where there is no radiator in the hall you are relying on waste heat from other areas to provide the feedback and shutdown. As this will vary depending whether doors are open or not you will probably find the boiler wastefully cycling on and off if the hall doors are closed with other rooms at temperature but the hall cool. With the doors open you may find the hall warming quickly and the stat shutting off before all rooms are to temperature.
If it is not a large or very draughty hall then leaving doors downstairs doors open a bit may work for you.

area that does not have a TRV. As TRVs shut down you would normally have an automatic bypass valve to continue to permit water flow through the boiler.

etc, Even with doors open you will find the rooms with heat sources will be warmer than those without. You may also get a better result by moving the stat to the upstairs landing.
In general don't put the stat in a room with additional heat sources, so kitchen (cooker) & lounge (people, TV) are out.
Take a look at the uk.d-i-y heating faq/wiki: http://wiki.diyfaq.org.uk/index.php?title ntral_Heating or other related sections at: http://wiki.diyfaq.org.uk/index.php?title=Special:Allpages
HTH
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