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Drayton TRV4 Snapped off - Any clues?

Discussion in 'Plumbing and Central Heating' started by Vyker, 30 Dec 2019.

  1. Vyker

    Vyker

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    upload_2019-12-30_12-31-59.png

    Anyone know how to salvage this? looks like the screw thread part of the plastic is left inside.
    I _really_ dont want to drain the whole system for this.
    Please let me know if anyone can help with ideas on how to get the plastic out. I'd like to just buy a replacement head and pop it on.
    Thanks in advance.
     
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  3. Gasguru

    Gasguru

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    Unscrew the ridged ring and replace the head...although given the spindle condition it might be more prudent to buy the complete valve and just use the head for now.
     
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  4. Nige F

    Nige F

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    As Gasguru says + press the spindle down to see if it moves - don't pull it out. Looks like the leaking spindle has released something that has attacked the plastic
     
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  5. mjgreen81

    mjgreen81

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    I have the exact same thing in my house. I have no less than 3 of these Drayton TRVs in exactly the same condition. 2 of them have been broken for a couple of years but are in rooms where I don't need to adjust the temperature.

    I just went to fiddle with the one in the bedroom which broke recently (as I want to turn the heat down) and tried to turn the spindle. It didn't really do anything. Worryingly I noticed that if I turn the black plastic thing at the bottom of the spindle it leaks a tiny bit of water (so i turned it back!)

    It's like the the heat causes the plastic to become brittle and eventually snaps. Not a great design!

    I think I am going to try and survive through winter and then drain the system and replace them all in the spring.
     
  6. mjgreen81

    mjgreen81

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  7. Vyker

    Vyker

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    Thanks for the comments, I didn't realise that it could just be screwed off from the metal part, I thought I the screw was in the plastic part.

    Did that head only come with the Drayton key? did it also come with any spare values?

    This video helped.
    In that video he talks about balancing, ensuring -11c from flow to return. Does anyone know how specifically 11c?

    Thanks
     
  8. mjgreen81

    mjgreen81

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    The head came with nothing else. See photo:


    I simply needed to unscrew the old silver ring, screw on the new head (setting to max heat to make it easier) and job done! Took 5 minutes.



    I've turned it right down to off now. Once I confirm that it has done the trick and the radiator is cooling down, I'm going to buy another couple of these for my other broken ones.

    On the topic of balancing, this is something I have always had to do on my system. However, I have never changed anything on the boiler, I have just used trial and error to set the appropriate temperature on the rads in various rooms. This normally meant that the first couple of rads on the system closest to the boiler would have the temp set low (but actually the rads were still plenty hot enough) and the rads furthest away from the boiler would have thier temp set higher. As I day though, it was trial and error and took me a couple of winters until I got the correct balance across the house.
     
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  9. ianmcd

    ianmcd

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    just balance the radiators using the Lockshield valve at the other end of the radiator
     
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  11. ericmark

    ericmark

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    That's expensive, you can get a programmable head for less than that, google eQ-3 TRV head.
     
  12. Vyker

    Vyker

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    That's what I had though, thanks for confirming.

    Any clues why -11c is needed?

    Need to get myself some of those clip on termostats
     
  13. ericmark

    ericmark

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    In my mothers old house, I fitted programmable TRV heads, however the TRV on many radiators was on the return, the result is unless the lock shield valve is carefully set the TRV will over shoot. In my case the TRV reports target and current so just turned the lock shield valve down until the current did not exceed target.
     
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  14. denso13

    denso13

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    It depends on a number of factors including the boiler type as a condensing boiler works best with a bigger difference. Although you may then need larger radiators. If your heating is working ok don't worry too much about the temp difference.
     
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  15. D_Hailsham

    D_Hailsham

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    11C is historical; it was originally 20F, which was supposed to be the optimal flow/return temperature differential for old cast iron boilers. Modern condensing boilers ofter specify a differential of 20C as this (a) reduced the head loss in the heat exchanger (cast iron boilers had virtually no loss), (b) the return temp was nearer to that required for condensing (approx 55C), assuming a flow of 75C.

    In any case, balancing all radiators to the same temperature differential assumes that each radiator exactly meets the heat loss requirement of the room - very unlikely.

    What you need to get are called thermometers, not thermostats.
     
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  16. Gasguru

    Gasguru

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    Old school....180 Fahrenheit - 160 Fahrenheit = 20 difference or 82 Celsius - 71 Celsius = 11 difference
    But as mentioned modern boilers have a huge heat exchanger resistance and to reduce pumping losses (and drop the return temp) we now work around a 20 degree drop...in fact at design temperatures an 11 degree drop would be almost impossible to achieve without a massive pump.
     
  17. ericmark

    ericmark

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    I had the same problem, what I did was compare target to current once the system has been running for some time, if target is below current then close the lock shield a little, and if target is above current then open the lock shield a little. However to do this clearly you need electronic heads which report both target and current temperatures. Screenshot_20190725-114727_MiHome.jpg With cheaper TRV heads it only shows the target, 510VC3xAYwL.jpg so you need a thermometer to get current, I have found thermometers can give up to 10°C different readings depending on where placed in the room, in my living room at this time, windowsill above radiators shows 18.3°C and the two TRV heads show 19°C and 20°C with target at 19°C since the TRV has 1°C increments that's about as close as one can get. So put a thermometer some where near the TRV so should be around the same 61dmtMm13BL.jpg air temperature and do some trial and error adjustments until you know if the TRV reading is accurate, the TRV head shown has an offset adjustment ± 3.5°C where the more expensive heads have twin sensors one for air and one for water so auto compensate.

    I am honestly not sure if worth the extra money for expensive electronic TRV heads, because there are some features of the cheap heads like window open detect and warning if pin is either not opening fully or not closing fully which are not on the more expensive model, also being able to set eco and comfort so just press one button on starting to use room, well two buttons one to turn to comfort other to work boost 80% open on valve.

    I have a draw full of new tower TFC group heads which will likely never be used, not a clue what temperature 3.5 is? I have an old TRV complete room at 19.9°C and it starts to allow flow at 2.3 approx. The newer Tower head on same valve starts to pass at 3 and not fully open until 4, which is not surprising as the old mechanical heads don't motor full range of pin and self adjust like the electronic type. But the old Mistral does seem to have a narrower band between starting to allow flow and stopping flow.

    I have a Tower unit in my hand warming it up, so just passing set to 20°C suspect hand will heat to 30°C but more interested in time, and it took 2 minutes to close, and with just 1°C difference it would clearly take much longer, so within 5 minutes a radiator can go from cold to full heat, unless you use lock shield valve to slow it down, really want it to take around 10 minutes to give TRV chance to close.
     
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