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Discuss What is this coil for? in the Plumbing Forum area at

  1. Stigster

    Stigster Plumber

    Sorry for the less than ideal photograph but it's all I've got to go on at the moment. One of my colleagues is having some trouble with his DHWS and I'm going to take a look on Friday.

    He showed me this picture and says under the black insulation is a coil of 15mm soft copper tube which is sat on top of his copper cylinder. It is connected to the hot water distribution pipe at that compression coupling. I believe the other end of the coil goes off backwards into the wall, to where I do not know.

    I have no idea what this external coil is for. Does anyone recognise it and know its purpose?

  2. Rob Foster

    Rob Foster Top Contributor!!

    no piccy yet .
  3. Stigster

    Stigster Plumber

    My link doesn't work? Can you see the Imgur link at all at the bottom of my post?

    The link is even showing in your quote of my post.
  4. Rob Foster

    Rob Foster Top Contributor!!

    ok got it, never ever seen this
    fascinating someone on here will know. centralheatking
    ukpf is never defeated
  5. bogrodder

    bogrodder Plumber GSR Top Contributor!!

    Preheat or
    A crude heat exchanger for a heat pump or thermal solar?
    • Like Like x 3
  6. Stigster

    Stigster Plumber

    That's certainly a sensible guess. As I mentioned before, I'm going to take a look on Friday and I'll let the forum know what I find.

    I have very few details as the guy I'm helping is a wood butcher (joiner) and has no knowledge of plumbing systems at all. He's got hot water at a good temperature at the cylinder and outlets except the bath mixer where it only ever gets luke warm, if that, he says.

    This was his "helpful" picture of the cylinder he gave me. It's impossible to diagnose these problems remotely so I've given in and I'm going to get eyes on the job.

    I think he maybe has unbalanced hot and cold supplies and that's why he's not getting blended hot water from the mixer but I'll know more in a couple of days.

    Thanks for looking.
    • Like Like x 4
  7. Stigster

    Stigster Plumber

    Right, I've been to take a look at this hot water problem. The system is working as it should. All that was happening was they were using up all the hot water from what is a fairly small cylinder when the fellow came home from work and the 2nd hot water heating time was set wrong for their usage. Set to come on at 4.30pm and off at 7pm. The fellow was coming home from work and having a long shower at around 6.30pm and his wife was expecting to run a full bath after 7pm but the cylinder was obviously not calling for heat after 7pm.

    I set it to heat water up until 9pm and that should sort it if she just lets it recover for a while after his shower.

    The coil on top is still a total mystery to me. All it is doing is making the hot distribution pipe longer by having the hot water flow through it when a tap is opened. It is a 22mm coil, not 15mm as I was originally told. Nothing else is connected to it, no solar, no heat pump, no nothin'. It just goes off to the hot outlets in the house.

    I was really hoping someone on here had seen one installed and could explain its purpose as I can find no other system like it. Why would you want the hot water to take a longer path than necessary? We normally try to do the opposite! It would stop some heat loss from 1 pipe circulation but normally the 450mm minimum horizontal pipe on the distribution pipe takes care of that.
    • Like Like x 2
    Last edited: Mar 22, 2019
  8. Rob Foster

    Rob Foster Top Contributor!!

    Thanks for the update and extra info. It really is a puzzle
    So...this is basically a plumbed in coil on top of a cylinder which passes domestic hot water from the cylinder thro this coil to the bath shower etc
    hot water taps....yes. So it is only warm hot when hot water is being drawn and of course the heating system is running. centralheatking.
    • Agree Agree x 1
  9. Mastermixlee

    Mastermixlee GSR

    Only time I've seen something remotely similar was when a diyer thought It was ingenious to run a large square coil with offset elbows that would pre warm the towels he had on slat type shelf directly above. He didn't take into account at the time for the excess draw off volume or the fact he then had to set the hot water stat on the cylinder higher to account for the heat loss.

    I mentioned to them that the cost they'd spent on copper and fittings plus the heat loss and additional water bills from longer hot draw off times would of been capable of running an electric towel rail for less money and hassle :rolleyes:

    But with this one being insulated it doesn't make any sense at all:confused:

    One of the unsolvable mysteries it seems... Which seems rare for members of this forum.
    • Informative Informative x 1
  10. Rob Foster

    Rob Foster Top Contributor!!

    Mastermixi ..I think you have got it right. This can be the only function of this bizarre set up...AND its probably not an installation that should be advice is to dis connect scrap it ..get some lolly from your scrap local merchant and get back to normal

    unless its a yorkshire dave special project...they do funny
    types of plumbing over the pennines !!!

  11. Roy_66

    Roy_66 Member

    Perhaps they liked a nice warm airing cupboard for drying stuff but didnt want the water at the taps to be burning hot ?
    • Like Like x 1
  12. YorkshireDave

    YorkshireDave Plumber Top Contributor!!

    It was a Yorkshire ruse to use up useless extra pipework. We told him it would create a venturi effect to speed up drying of towels.
    A bargain at only £8,000,047.33
    • Funny Funny x 2
    • Like Like x 1
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