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Should I open the lever valve a bit to get more flow to my furthest rads?

Discussion in 'Plumbing and Central Heating' started by pedr0, 18 Mar 2021.

  1. pedr0

    pedr0

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    I did a lot of balancing of rads in our house, but by the time I got to the final rads furthest away from the boiler, I just couldn't get the right temp drop even with the lockshields wide open. In fact one of those three rads struggles to get any significant heat at all.

    I wonder if there isn't quite enough flow? I notice that there is a lever value that is half closed in the main boiler room - it's just before the radiator zone valve. See the picture below.

    Should I open that lever valve on the radiator flow a bit more?
     

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  3. muggles

    muggles

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    Worth a go. Lever valves aren't really suitable for use as balancing valves anyway, if indeed that's what they're being used for
     
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  4. pedr0

    pedr0

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    Thanks muggles

    No idea why it's half shut like that. The original installer went bust before commissioning so someone else filled up the rads and commissioned it but didn't have time (inclination?) to do all the balancing. Can't be sure which one of them put the lever at half way, but suspect it was the original installer.

    Didn't want to touch it without asking first though in case it was for something important.

    Would you suggest just opening it up completely, or just maybe 3/4 open and see if that helps?
     
  5. Madrab

    Madrab

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    Have to agree there, using those lever valves is really quite a half a$$ed way of balancing a system and is not the normal way to control the flow in a central heating system.

    The UFH should be controlled by flow meters as part of the manifold and the flow and returns should be open and the wet CH properly balanced locally at each rad.

    Do remember balancing isn't just about getting the desired temp drop across the rad as much as ensuring that the rads each receive adequate HW at roughly the same time to allow them to warm up equally.
     
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  6. pedr0

    pedr0

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    Thanks Madrab.

    I've got just one underfloor heating area - in the kitchen. It's handled by a wunda manifold which has three loops, each with their own flow meter. I was able to get the UFH balanced quite nicely at the manifold. There are lever valves on the UFH in the boiler room too and in that case, both the flow and return are half open. But I left them alone because I was able to get the UFH balanced and working well. Is there anything bad about leaving the levers half closed on the UFH flow and return? - E.g. if I open the Rad lever valve, but leave the UFH lever valve half closed, will that deny the UFH of any hot water whenever the rads call for heat?

    As for the CH, I am indeed balancing at each rad. Working from the one that heats first and getting its temp drop at 12 deg, and then on to the next etc. I was working on the understanding that that approach would result in the rads heating up at the same time. Is that an oversimplified/optimistic understanding?
     
  7. Madrab

    Madrab

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    Without actually being onsite and seeing the system in it's entirety then it's difficult to see why the valves are there and why they've been set the way they are.

    When balancing a complete system, the starting point is everything fully open when it comes to the main flow and returns as there's very little real control using the lever valves.

    I wouldn't be worrying about the temp drop until getting all the rads to heat up properly, once that's achieved then look to fine tune the temp drops across the rad.
     
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  8. dilalio

    dilalio

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    Are your rads new(ish)?
    You want to be looking more at a deltaT of 20-22°c but it's not law. (yet).
     
  9. pedr0

    pedr0

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    Yes, rads are new (3 years) but traditional cast iron style.
     
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  11. pedr0

    pedr0

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    Oh - never come across this before. So rather than thinking about a 12 deg drop across the rad, I should be thinking of achieving an average rad temp?

    E.g. target room temp is 20deg
    Target deltaT = 20deg,
    deltaT = average rad temp - target room temp
    Therefore, average rad temp = 40 deg

    Average rad temp = (temp at in - temp at out)/2
    If temp at in = 60deg, then to achieve an average of 40 deg, the temp at out would be 20 deg.
    Which means a whopping 40 degree fall from one side to the other and the temp on the out being as cool as the room itself o_O
    I think I must have either understood deltaT incorrectly, or be running my rad input too hot.

    Or does deltaT just mean the difference between input temp and output temp of a rad. I.e. are you saying that I should be aiming for 20 degrees across the rad rather than 12?
     
  12. Nige F

    Nige F

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    Just feel them then(y) delta, schmelta.;)
     
  13. D_Hailsham

    D_Hailsham

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    The deltaT (difference between flow and return temperatures) of a radiator is nothing to do with how old the radiators are. It is determined by the boiler. Older boilers, with cast iron and similar heat exchangers, were designed for a 10C/11C differential. Modern condensing boiler, with very narrow pathways, are designed for differentials up to 20C. This means the flow rate is halved so the head loss is reduced by a factor of 4. A smaller pump can then be used.

    Which boiler do you have (make and exact model)?
     
  14. dilalio

    dilalio

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    I didn't say it was.
    I asked about his rads to get a sense of how much control he would still have over their operation. Perhaps I should have said valves, but, hey, you know, language and stuff!
     
  15. dilalio

    dilalio

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    Not just the boiler.
     
  16. pedr0

    pedr0

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  17. D_Hailsham

    D_Hailsham

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    The reason the last rad was unable to get hot could be that the bypass valve in the boiler had not been adjusted for your system. It has a default setting of 250mb but can be set between 170mb and 350mb. you would need it turned up, possibly on 10-20mb (one -two turns). Unfortunately this is internal to the boiler so it needs to be done by a Gas Safe person.

    The radiators look nice. There are reports that this type of radiator works very well with condensing boilers (when they are condensing).

    It's a pity the TRV manufacturer does not provide any technical spec for their products. It's impossible to say if they meet the required standard.
     
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