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Location of radiator without TRV

Discussion in 'Plumbing and Central Heating' started by critor, 27 Sep 2020.

  1. critor

    critor

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    Hi all,

    I understand that a CH system requires that at least one radiator have no TRV to prevent the user from closing all valves, and overheating the system, but I have also read on this forum that the radiator lacking a TRV is typically placed near the thermostat (https://www.diynot.com/diy/threads/why-1-radiator-without-trv.30297/).

    Perhaps there's a sensible reason to do this in general but I suspect that there are good reasons not to place it near the thermostat.

    The front of my house is typically a few degrees warmer than the rear due to a conservatory that is very lossy. The house was built 4 years ago and the conservatory (more like an extension with a glass ceiling than a proper conservatory) is part of the original design.

    The thermostat is also in the front of the house and so is the TRV-less radiator.

    It strikes me as odd because in a house with such a dramatic thermal imbalance I think it would have more sense for the TRV-less radiator to be at the cold end of the house.

    The obvious issue with it's current placement is that despite my efforts to balance the normalise the temperature gradients by fully opening the radiators in the cold areas, and partially close the ones in the warm areas, the TRV-less radiator is disproportionately heating the small corridor where the thermostat is.

    Inevitably that small volume of air gets warmed quickly (even though the TRV-less radiator is the only radiator in that zone), the thermostat switches off, and the cold part of the house remains cold.

    My questions:

    1) Is there any reason why I shouldn't remove a TRV from one of the radiators in the cold zone and fit it on the radiator near the thermostat?

    If the TRV-radiator is part of the same circuit, I suspect that would be fine. But if it has it's own circuit that could cause overheating if all TRVs were closed.

    2) Is it standard practice for the TRV-less radiator to be in it's own circuit?

    Thanks.
     
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  3. Madrab

    Madrab

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    It's not true now that at least one radiator must have a TRV fitted, automatic bypasses are fitted to a CH system now to ensure correct flow through the boiler to avoid overheating.

    The fundamental reason for not having a TRV on a radiator close to a thermostat is that the 2 temperature controls will battle against each other one switching off the heat emitter, the other switching off the whole system. Typically though the thermostat and rad with no TRV would be placed where it is considered to be the coldest area in a house, that's typically the hall.

    It wouldn't be normal to have 1 hall radiator in a zone all of it own.

    Sounds like their design is a little out of whack if the heat loss to the rear is that significant and it may be an idea to at least looking to relocating the thermostat. Does the conservatory have a door access to the house that can be closed, reducing the heat loss from that area?
     
  4. jackthom

    jackthom

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    The simplest thing to experiment with would be to almost close off the lock shield valve on the radiator where the thermostat is located so the small hall takes much longer to get up to temperature and the rest of the house has a chance to warm up before the thermostat switches off.

    If that doesn’t work then I’d think about moving the thermostat to the cooler living area you spend most time in.
     
  5. ericmark

    ericmark

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    As @Madrab says the two thermostats can battle for control, but also they can work in unison. The TRV can control room temperature better than the wall thermostat as it is where the thermals will circulate the air, and with programmable TRV heads they can nearly do all the control required.

    However they have one problem, they can't by water temperature control stop the boiler cycling when no heat is required. So some where you need a wall thermostat/programmer/hub to tell boiler when it is not required.

    The books say the wall thermostat should be in a cool room with no outside door, on the ground floor, with no alternative form of heating, that includes the sun shinning in a bay window, and that a TRV is not required in that room. However the room rarely exists, so in my case the hall has both a wall thermostat and a TRV both programmable and set so the TRV is slightly cooler than the wall thermostat, so the wall thermostat only switches off on warm days.

    I will admit setting the hall wall thermostat, lock shield valve and programmable TRV to work in unison took some time and tweaking, and although the TRV can be set to geofence, I have never bothered, only the wall thermostat has geofencing set, this does mean when I have been out for the day, on return the heating does tend to over shoot slightly, there is no wifi link between the wall thermostat and the TRV, I did try it, but it failed to work as wanted.

    There are systems where the TRV head can talk to the wall thermostat, drayton, honeywell, tado all make systems, and I will guess with a gas modulating boiler an opentherm wall thermostat and linked TRV heads is the bees knees, however I don't have an opentherm gas modulating boiler, there are three odd ones out with the wall thermostats.
    Hive does not have opentherm, but has a demand for heat system with the TRV heads so in winter will not turn off.
    Nest does not connect to TRV heads, but does have opentherm and a good algorithm, it is what I have but will admit not linking to TRV heads seems short sighted.
    EPH which can have multi wall thermostats set as master and slaves to work with opentherm, designed for zone valves, but seems does not link to TRV heads?

    However I find using cheap programmable TRV heads like eQ-3 (I paid £15 for blue tooth model, no blue tooth £10 each) and setting the same program as the wall thermostat in same room works near enough, and in hind sight realise a cheap £35 programmable wall thermostat and eQ-3 TRV heads would have likely worked just as well as my expensive Energenie TRV heads and Nest Gen 3, the only advantage is auto switching off when leaving house and back on with return and using the temperature shown on the TRV to switch on the AC before returning home in the summer.

    I have now lived in 4 houses, one hot air so does not count, one open plan so a single wall thermostat downstairs with no TRV's down stairs and only TRV's upstairs, and two with halls and doors on the rooms, and both had wall thermostat in the hall, both took some setting up and tweaking, but both in the end worked well, not perfect, but well.

    The one with gas had the wrong wall thermostat, it had anti-hysteresis software which turned boiler off/on as target was approached to stop over shooting, which was wrong thing to do with a modulating gas boiler, it worked A1 but had a different wall thermostat been used it would have likely used less gas.
     
  6. durhamplumber

    durhamplumber

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    You are seriously over complicating it.
     
  7. critor

    critor

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    Thanks to all the suggestions and feedback. It's much appreciated.

    I did consider replacing my wired thermostats with a Hive or alternative and place them in more strategic places (cold parts of the house) but didn't want to go through the bother of deciding on what to buy. Plus I thought it would be quicker and cheaper to just swap TRVs around.

    I'll try jackthom's advice and reduce the lock shield valve. And if that isn't enough, consider one of the more involved suggestions posted.

    Thanks all!
     
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  9. stem

    stem

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    Not sure how they would work "in unison" in reality.

    Scenario 1. - If the TRV is set lower than the room thermostat, the TRV will switch the radiator off before the room is warm enough to satisfy the room thermostat, so the room thermostat will never switch off and is rendered useless, leaving the heating system running continually without a boiler interlock facility.

    Scenario 2. - If the if the Room thermostat is set lower than the TRV, the Room thermostat will switch the heating off before the room is warm enough to operate the TRV, so no point in having it.

    Scenario 3. - Set them at the same level so that they operate together. In practice as one is an analogue device, and one is digital, plus they are at different positions in the room, mighty difficult to achieve, and if you were able to manage it, adjusting them both to keep them in step would be a task too far for most people.

    Unsurprisingly then, thermostat manufacturers often state that their products should not be installed in the same room as a TRV. Some will even explain why.....

    Energenie MiHome
    [​IMG]

    Hive
    Hive.JPG

    I've lost count of the number of times I've been asked to look at a thermostat that 'isn't working' only to find it's in a room where the radiator also has a TRV on. Once the TRV has been removed all is well :)
     
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  10. ericmark

    ericmark

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    My original scenario is Energenie MiHome thermostat (TRV) is put on radiator in hall near to the front door, the wall thermostat is more central between the doors to other rooms, in the winter the wall thermostat never turns off, except when there is a reduction in temperature, so at 10 pm when both TRV and wall turn down to 17°C over night the wall thermostat will turn off the boiler. Most nights it will stay off, as the house rarely cools that much, so really the same as having a programmer, in the morning TRV turns to 19°C and wall thermostat turns to 20°C and the wall thermostat in winter will never turn off, so all control done by the TRV, and the boiler will modulate, keeping all rooms not just hall at the temperatures set, as you say the wall thermostat does nothing more than a programmer except on very cold nights when it will reactive the boiler.

    However as spring arrives on a warm day, instead of the boiler starting to cycle off/on as it can't modulate low enough, it will be turned off by the wall thermostat, so the boiler only runs on cool days as the summer approaches.

    The scenario today is not as good, as the boiler will not modulate but only cycles, so the wall thermostat does the controlling of the boiler using the lock shield on the radiator to limit heat in the hall, the Energenie MiHome thermostat (TRV) was claimed to follow the Nest Gen 3 wall thermostat, however it failed, it was hit and miss if it followed, and it does work to an extent so radiator gets hotter if front door opened, and it does compensate to an extent, but will admit with a non modulating boiler don't really need a TRV in same room as the wall thermostat.

    Son's house is open plan, and has no TRV's down stairs, just one central thermostat, the TRV's upstairs are vital, without them opening a door will cause a room to over heat, but the Myson fan assisted radiator ensures movement of air so the three radiators in the two rooms keep the rooms at an even temperature. This will be first year with a modulating boiler, so not sure how the Myson will fair.

    So it does seem from the three houses I have lived in that there is no one system suits all.
     
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  11. critor

    critor

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    Thanks @stem for your detailed explanation.
    It makes sense and is intuitive. In particular Scenario 1 seems plausible except that I always have heating programmes for day/night and weekdays/evenings (so the boiler would be shut off during the nighttime and when we tend to not be home).

    That said, this will be the first winter where both my wife and I will be working from home. Previously it was only her and she used to close the door to the study and use a fan heater to avoid heating the whole house.

    With me working in the dining table (the cold part of the house) we'll end up heating most of the day or I may have to move my WFH "office" into one of the (already crammed) bedrooms.

    I guess using programmes is more or less what @ericmark does (but he also uses programmable TRVs) to avoid scenario 1.

    Also, my thinking was that if I restricted flow to the radiator near the thermostat (either by partially closing the LSV or adding a TRV), once the cold part of the house warms sufficiently, heat will flow to the front and eventually trigger the thermostat shut off.

    But I've since doubted myself because the reverse would be true: a heat differential would result in heat from the front transferring to the rear. That's not the case. What's probably happening is that any excess heat in the front that passes through the door leading to the rear will rise up the staircase, by-passing the rear ground level.

    I've attached a floor plan to (hopefully) help illustrate. The thermostat is on the diagonally oriented section of wall between the study and WC. The radiator is on the wall adjacent to the WC's door.

    So it seems I have a few options:

    1) Try reducing the LSV (or buy a programmable TRV) and rely on the programming of the thermostat to turn the boiler off.

    2) Get a wall mounted air source heat pump (A/C) fitted on the external wall of the conservatory to reduce the temperature differential. I considered this during the summer but was put off by prices - maybe A/C engineers will be more eager (and competitively priced) for work in the winter...

    3) Upsize the radiators in the kitchen/diner.

    4) Put up with it (continue cranking the thermostat to 24C to get something approaching 20C in the dining area).

    Thanks again.
     

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  12. ericmark

    ericmark

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    I was very pleased with the Energenie MiHome thermostat (TRV) in my mothers house where we lived before we came here, however at just under £80 a pair, why sold in pairs I don't know, with 14 rooms in this house I was not keen on the idea of doing all rooms with them. So I got 5 eQ-3 TRV heads at £15 each with bluetooth, I was a little peeved to find will only work with one phone, so wife controls two and I control three, however the design means I rarely use the phone, just press a button on the TRV, and non bluetooth are less than £10 each last time I looked.

    Now I prefer the eQ-3 one they have window open detect so auto turn off heating in kitchen when unloading food, and two don't need phone to switch from the pre-set comfort and eco modes. So walk into bedroom press button and moves from 17°C to 20°C. But not wifi so use the Energenie to monitor temperature of living room while away from home and decide if to turn the AC on, only a cheap AC designed to hang pipe out of window, but I have it connected to chimney so don't need to leave window open.

    Your house like mine, there is no room that really lends its self to fit a thermostat to control whole house, but with a modulating boiler all the thermostat is for is to switch boiler off on a warm day, it does not really control room temperature, so if the sun catches that living room bay window then likely that would be a good location, but I even fitted one in the kitchen, it brakes all the rules should not be in a room with outside door or alternative heating, however all it does it turn off boiler to stop it cycling on a warm day.

    As to setting radiators I had a problem in mothers old house, all the TRV's were on the return, so it got radiator hot before any heat reached the TRV head, so would over shoot, so I set the Energenie TRV to temperature I wanted say 20°C and two hours latter if not at 20°C I opened the lock shield valve, and if over 20°C closed it just a ¼ turn at a time, and I moved the Energenie TRV room to room as it showed both target and current so I knew exactly what the TRV was set at, and slowly adjusted each room so the TRV would get it to temperature I wanted, and I found once set, in the few rooms still with wax TRV's at around 3.5 the room was maintained at 20°C, when I came to leave the house all the Energenie TRV's were swapped back to wax, and it still worked well.

    The problem is you have a TRV marked *123456 so you have really no idea if 3.5 is 20°C so if room warm or cold you don't know if the TRV needs adjusting or the lock shield valve, but once a TRV head marked in °C was fitted then you know that is correct so only one item needs adjusting the lock shield valve.

    Before moving out of my mothers old house it was A1, the heating worked well, however this house is another story, the boiler does not modulate it simply switches off/on so the radiator temperature varies depending if boiler just about to switch off, or just about to switch back on, I started setting the lock shield then the plumber changed all the TRV bases as some were weeping so all lock shield valves were turned off and on, so starting again.

    Wife was ill in summer so had to get a Tommy thermometer it was only one I could find, so I am hoping I can use that to set the differential on each radiator? I would like to use just the TRV's to control temperature, but not sure how it is going to work out, only been in this house for one winter and the boiler had problems so not sure how much cool rooms due to settings and how much due to boiler cutting out.

    I seemed odd to me when I returned to mothers house, when I left still used coal fires, our first house was hot air central heating and since all air circulating temperature control all rooms was spot on, but blowing warm air at single glazed windows was expensive, second house open plan and again Myson radiator so air circulated, up stairs got too hot and had to fit TRV's upstairs, but both houses simply worked, so never really thought about central heating.

    It was only after returning to mothers house to look after her I realised some central heating systems don't simply work, every lock shield valve was wide open, and my dad had it seems given up and used a gas fire, but mother was sleeping down stairs, and without central heating her bedroom was an ice box, could not use gas fire it was too close to bed.

    Same applies to geofencing, until I moved here, always had a gas fire, so on arriving home gas fire plus central heating and room soon warm, here it is a coal or wood fire, think last people used wood, but lighting a fire is not fast, so for the first time relying on the central heating to warm house, and the extra ½ hour heating before we get home is nice, so now we appreciate geofencing.
     
  13. stem

    stem

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    The boiler interlock is also meant to turn the heating system 'off' when the heating program is set to be 'on' but the house has warmed up, so that when the room thermostat reaches the set temperature it will shut the heating system down completely. A standard TRV doesn't do this, all it will do is turn the radiator off, but the boiler will continue to cycle and the pump will run which wastes energy.

    Today as the weather is mild, my house has been warmed by the sun and the room thermostat has shut the heating down for several hours now, even though the heating program is still set to be 'on' If it only had TRV control the boiler would continue to run and keep itself, and the pipes / pump / motorised valve etc. connected to it hot.

    To illustrate the principle. You arrive home in your car. However as you are going out again in a couple of hours you pull the handbrake on to stop the car moving anywhere while you don't need it, but leave the engine running instead of switching it off.
     
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