Radiator question

Hi all.

I'm trying to understand why my lounge radiator never goes above 17.8 degrees (as measured by a freestanding temperature gauge sitting next to it).

My setup: the thermostat is in the hallway where there is 1 non-TRV radiator. I set this thermostat to 18. The hallway slowly climbs up to the required temp while the single non-TRV radiator in the lounge (see image) pumps out steady heat till it hits 17.8 - then it stops there and won't go higher.

The affected lounge radiator is partially behind a sofa, which means the bottom of the rad is going to have a lot of heat trapped down there. Even though the rad has no TRV, is it somehow sensing that it's waaay hotter than 18 degrees and so is turning itself off? Seems unlikely but I don't know what else it can be. 


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  • junglist_matty
    junglist_matty Posts: 86
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    What happens if you set your heating thermostat to 19degrees?
  • breaking_free
    breaking_free Posts: 753
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    What happens if you set your heating thermostat to 19degrees?
    I haven't tried that yet - I've never set it higher than 18. I'll test this out on the weekend if I'm home.
    "The problem with Internet quotes is that you can't always depend on their accuracy" - Abraham Lincoln, 1864
  • Albermarle
    Albermarle Posts: 21,062
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    What is the boiler flow temperature set at ? This is the temperature at which the hot water leaves the boiler to go around the heating system.
    Typically it is set around 70 degree centigrade, but can be higher or lower. Normally when the system is fully warmed up the radiators will be about 10 degree less than than the boiler flow temperature.
    It is possible to turn the boiler flow temperature right down on some models, so maybe this is what has happened by accident? 
    What about other radiators in the house, do they get a lot hotter ? Is it just this one that stays cool?
  • breaking_free
    breaking_free Posts: 753
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    What is the boiler flow temperature set at ? This is the temperature at which the hot water leaves the boiler to go around the heating system.
    Typically it is set around 70 degree centigrade, but can be higher or lower. Normally when the system is fully warmed up the radiators will be about 10 degree less than than the boiler flow temperature.
    It is possible to turn the boiler flow temperature right down on some models, so maybe this is what has happened by accident? 
    What about other radiators in the house, do they get a lot hotter ? Is it just this one that stays cool?
    Can confirm the flow temp is set to 70. I haven't put the temperature gauge beside any of the other rads as the lounge is that only place that I sit in for long periods. 

    So, does anyone want to comment on the guesswork in my initial post? "Even though the rad has no TRV, is it somehow sensing that it's waaay hotter than 18 degrees and so is turning itself off? Seems unlikely but I don't know what else it can be". I assume non-TRV rads don't work like this but would like it confirmed one way or the other if poss.
    "The problem with Internet quotes is that you can't always depend on their accuracy" - Abraham Lincoln, 1864
  • frugalmacdugal
    frugalmacdugal Posts: 10,077
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    Hi,
    breaking_free said:
    So, does anyone want to comment on the guesswork in my initial post? "Even though the rad has no TRV, is it somehow sensing that it's waaay hotter than 18 degrees and so is turning itself off? Seems unlikely but I don't know what else it can be". I assume non-TRV rads don't work like this but would like it confirmed one way or the other if poss.
    if it's a non TRV how can it sense anything it'll just go with the flow.
  • markin
    markin Posts: 3,717
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    edited 4 January at 4:54PM
    With a flow of 70c the return temp may just be too high so the boiler shuts off?

    With no fins on that rad it must have a poor output anyway, have you bled them all of air?

    Could the balancing need a little tweak still? 
    https://forums.moneysavingexpert.com/discussion/6411582/one-radiator-suddenly-switched-off/p1


    You want the return temp at the boiler to be under 50c for a condensing boiler to be condensing and run at close to 95%
  • Albermarle
    Albermarle Posts: 21,062
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     I haven't put the temperature gauge beside any of the other rads as the lounge is that only place that I sit in for long periods. 

    It would help to diagnose what the problem is, if it is affecting other radiators or not. You do not need a temperature gauge to tell the difference between 20 and 60 degrees ( which is approx what it should be ).

  • What happens if you set your heating thermostat to 19degrees?
    I haven't tried that yet - I've never set it higher than 18. I'll test this out on the weekend if I'm home.
    It sounds to me like there's nothing wrong, what you said:

    1. Your heating thermostat is in the hallway where there is 1x non-TRV radiator.
    2. In the living room there is a non-TRV radiator  and a freestanding temperature gauge to measure ambient air temperature.

    You set the heating to 18, and the system turns on, the thermostat regulates the boiler to maintain 18 (in the hallway). Other rooms in the house will not all be the exact same temperature, because: radiator might be turned off, rad might be too small for the room, it might be clogged with sludge, it might need bleeding, the room might be drafty, the windows might be less efficient etc.... there are loads of possibilities. 

    However, you say your thermometer reads 17.8, that's pretty close to the target. Maybe the thermostat isn't calibrated, or maybe your thermostat is calibrated slightly high etc.... if you set 19 and see what happens in the living room, I suspect the thermometer will read 18.7 or 18.8.


  • ThisIsWeird
    ThisIsWeird Posts: 4,458
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    edited 5 January at 6:54AM
    Sounds like what junglist says. It's working normally, but it just needs tweaking.
    Like JM, I assume that '17.8oC' refers to the room's temp, and not the rad's.
    BreakingFree, a Q - when the sitting room rad initially comes on, is it 'hot' to the touch? If 'yes', then almost certainly there's nothing wrong, but you just need to tweak things.
    The two tweaks you can do are:
    1) turn the hallway room stat up a degree or more. (Drawback - the hallway will now become warmer than you may want, so a waste of energy.) Your sitting room should also become warmer as your boiler will be on for longer.
    2) turn the hallway rad down a small amount so that it outputs less, so takes longer to get the hallway up to 18oC. That way the sitting room rad will have more time to get the sitting room warmer. (This is the 'proper' tweak. But, the sitting room rads should really have TRVs on them).
    Better still, imv, is to move the hallway stat into the sitting room, almost certainly easier than you may fear. This is the best way to get the most important room in the house to exactly the temp you want, and every other room can be adjusted separately without affecting this. Show us your stat if you fancy doing this. Seriously, the best method. And, you can consider going 'Smart' at the same time. You will giggle with delight as you sit watching BBad, and control the room's temp with a touch of your phone. You will, you will...
  • FreeBear
    FreeBear Posts: 14,244
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    ThisIsWeird said: 2) turn the hallway rad down a small amount so that it outputs less, so takes longer to get the hallway up to 18oC. That way the sitting room rad will have more time to get the sitting room warmer. (This is the 'proper' tweak. But, the sitting room rads should really have TRVs on them).
    A longer term "proper" solution is to install a larger radiator in the lounge and make sure all radiators have TRVs fitted.
    Depending on the current flow temperature and exact make/model of the lockshields in the hallway, it may not be possible to dial that radiator back by much.

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