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Heated towel rail not getting hot from immersion heater

Discussion in 'Plumbing and Central Heating' started by Triffle, 12 Oct 2019.

  1. Triffle

    Triffle

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    Looks like it's time for me to break out MS Paint again :LOL:, this time to ask a plumbing/heating question.

    We currently have the following setup for our hot water:

    Oil-fired (gravity-fed) Rayburn with hot water cylinder above (cylinder has an immersion heater).
    Water is supplied from cold water tank upstairs.
    One heated towel rail in bathroom downstairs.
    There are no other radiators in the system.


    When the Rayburn is on it provides hot water to 3 sinks (1 upstairs and 2 downstairs), and it heats the towel rail nicely.

    But, we are in the process of 'decommissioning' the Rayburn (in other words our oil tank needs replacing, and due to latest rules and regulations it is an absolute pig to replace it, hence we've decided to do without the Rayburn altogether). Shame really, as there's nowt wrong with the Rayburn itself.


    So my problem is that now, with just the immersion heater on, we are still getting our nice hot water at our sink taps, but the towel rail can at best be described as 'lukewarm'.

    Here is a diagram I've knocked up to show the system as it is:
    upload_2019-10-12_13-7-50.png

    Now, in my (admittedly rudimentary) understanding of plumbing and heating, I figure that the action of the Rayburn heating the water 'pushes' it up into the HW cylinder, then around in a sort of loop which includes the heated towel rail, then back into the Rayburn again...

    ... if this is completely wrong then please correct me! :)

    So, I'm then guessing that when the Rayburn isn't on, there isn't this 'pushing' action moving the water around the loop.

    If I'm right so far, I'm wondering if there is a pump of some sort that could be attached to the pipework (I'm thinking it would likely go near where the Rayburn is, on the blue pipe going up?) which would emulate the action of the Rayburn?

    Would that be possible? (And if so, is it just a matter of attaching it to the pipe and to an electricity supply, or is it something quite complicated?)

    Or is there some other reason for our lack of towel rail heat?

    Hopefully my diagram above provides enough information but if I'll of course answer any more questions if need be.
     
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  3. Tigercubrider

    Tigercubrider

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    I am not a plumber
    But normally (afaik) the water in the boiler/Rayburn does not mix with the water in the hot water cylinder. The heat source heats a coil immersed in the cylinder and heats the tap water by means of contact.-as does the electrically heated immersion heater.

    If you have a heated towel rail then the water in the sealed circuit that heats the water between the hot water tank and boiler passes through the towel rail. You don't wash in the towel rail water

    You can buy immersion heaters that fit to a heated towel rail to supply warm towels when the boiler is off
     
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  4. Madrab

    Madrab

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    Not being familiar with an oil fired Rayburn I will happily bow to the oil chaps on here but I wouldn't like to think that your hot water taps are fed by the same water that runs through the HEX in the Rayburn and through a towel radiator, who knows what kind of contaminants could be introduced.

    I would suggest that they will be 2 separate systems and the water heated by the rayburn would run up into a coil in the HW cylinder and that also feeds out to the towel rad (there as a heat sink, once the cylinder is hot) and then back to the rayburn.

    The hot water in the cylinder is heated by the coil and then goes out to the outlets.
     
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  5. Hugh Jaleak

    Hugh Jaleak

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    I'd hazard a guess the system is a bit more involved than you realise, and the towel rail is heated from the 'primary' circuit, i.e. a closed loop of the system that heats the cylinder from the Rayburn. This keeps the water in the Rayburn the same and prevents corrosion. Heat is transferred into the Secondary system (i.e. the water you'd get out the hot tap), by means of a Heat Exchanger inside the HW cylinder.

    Using the immersion, whilst heating the secondary system, will not put heat into the Primary side. Additionally, the Primary side operates by Gravity Circulation, you are probably effectively now asking that to work in reverse.... ;)
     
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  6. Triffle

    Triffle

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    Hmm, ok, that's making sense, thank you so much for quick replies, it is much appreciated.

    So basically, there is a pipe going through the hot water cylinder, containing the same water as in the towel rail, and this pipe (I'm picturing it being something like the element in a kettle but with water inside it) heats the water in the cylinder, and that water goes to the taps?

    So only the Rayburn can heat the water within this 'element pipe'?

    I've just done a quick search for heating elements mentioned... is it this sort of thing? https://www.screwfix.com/p/towel-radiator-element-400w/88595
    ... because if so, that won't fit on our towel rail because the drain plug (where this seems to fit in?) is not opposite the long pipe of the towel rail, so it wouldn't fit.

    So... are there any other options, as I'm now seeing that a pump isn't the answer? (It would just be pumping lukewarm water around the primary system, I see that now!).

    Could the immersion heater element as per the screwfix link (or something similar), be installed elsewhere in the primary circuit loop, thus heating that water? Or would it then still need a pump to circulate the heated water around?

    Just trying to think of options..
     
  7. Madrab

    Madrab

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    Yes, the reason for the towel rad getting slightly warm will be the hot water in the cylinder (for the taps), heated by the immerser, is heating the water in the coil that then convects slowly to the rad.

    Once the rayburn is removed ..... could you fit a pump, wired to a switch, into the primary pipework and then use the hot water heated by the immerser in the HW cylinder, to heat the water running through the coil in the cylinder and ergo the rad (like a thermal store) .... then yes I guess you could, not very efficient though I wouldn't think and would need a bit of balancing to get the temp right.
     
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  8. Triffle

    Triffle

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    Thank you. We shall have to look into whether it's worth putting in the pump because as you say, it's not going to be very efficient.

    At least I have a better understanding of the system now so thank you to all who helped out :)


    One final question - what is the best way of dealing with the pipes, because at the moment (as per my diagram) one pipe comes up from the floor and goes into the Rayburn, then a pipe comes back out at the top of the Rayburn.

    The plan is to connect these two pipes together, outside of the Rayburn, so that the loop remains intact and the Rayburn can then be removed.

    The water would have to drain out of it as we disconnect of course so we'll turn off the feed to the cold water tank (and we'll be sure to turn off the immersion heater!!) but looking at the pipework it should fill up again from the cold water tank feed, once the loop is reconnected..

    .. any flaws in that plan? Possibility of air locks etc?
     
  9. Madrab

    Madrab

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    Always a possibility of airlocks, you should have a bleed point on the pipework at it's highest point. You can always bung the cold water cistern in the attic and cap the vent to minimise water loss.

    That being said are you sure the cold water supply to the HW cylinder is the same as the cold feed to the primary heating circuit, it may be different.
     
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  11. Triffle

    Triffle

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    Ooh I'm not sure now...
    • There's one pipe coming up from the top of the Rayburn, into the side of the HW cylinder, fairly near the top (red one on my diagram).
    • Then there's the one which comes down from the cold water tank and into the side of the HW cylinder near the bottom (filling the HW cylinder I think), and also continues down to the bottom of the Rayburn and the pipework under the floor (blue one on my diagram).
    Does that certainly mean that is is the same supply? Or do you mean there could be another supply into the 'loop' that we can't see at the moment (e.g. coming in somewhere at the top of the loop in the ceiling)?


    EDIT: I'm sitting here reading online about Direct and Indirect heating systems... trying to figure out if indeed there is this heating element inside our cylinder or not.

    According to this link https://www.diydoctor.org.uk/projects/domestic_hot_water_systems.htm

    :confused: We only have one water tank in our loft.
    Also, earlier in the year we replaced the immersion heater in the cylinder as the old one was corroded on the outside... and I don't remember my husband seeing a heating element inside. (It isn't a very big cylinder).

    And it is quite an old system.

    Also this link http://www.smrbathrooms.co.uk/acatalog/Heated-Towel-Rails-FAQ.html suggests it is possible to have the same water in the towel rail and the taps

    I'm not trying to contradict what I've been told on here, I'm just keeping an open mind and trying to fully understand what system (or hotch-potch of systems!) I've got :oops:


    Or, does the fact that the towel rail only gets lukewarm now, 'prove' that there is an indirect system in place (because of what Madrab said in post 6)? (Or could there be another reason for that)... sorry for my rambling thoughts... is it lukewarm because, unlike a hot tap, there is nothing 'pulling' the hot water through?
     
    Last edited: 12 Oct 2019
  12. Madrab

    Madrab

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    No it may be that the pipe is shared but I would be surprised if it is. Time to track and trace the pipework methinks.

    Usually the cold feed to a central heating system would be completely separate from a feed to a hot water cylinder to avoid any backflow contamination into water that may be used for human use. That why an open vented central heating system (which your system essentially is) would have it's own feed and expansion tank separate from the cold water cistern that would normally feed an open vented hot water cylinder. Speaking of open vents, I don't see any of them in your diagram.
     
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  13. Nige F

    Nige F

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    OP could you (or rather a HETAS person )convert the Rayburn to logs/solid fuel ? they started off like that
     
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  14. Triffle

    Triffle

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    OK thanks, it does seem a confusing system we've got as it doesn't seem to fit either description fully. There is definitely only one cold water tank in the loft (no separate expansion tank), and it does appear that the cold water feed pipe going into the cylinder is the same one that goes further down and into the Rayburn, so they don't seem separate. Plus my husband has confirmed that he did not see a heat exchanger coil element inside the cylinder when he replaced the immersion.

    But yes, we will need to investigate further :) (trouble is the top of the cylinder goes into the ceiling so it isn't easy to see what pipes are coming out of the top (well there is only one, and we know it goes across the ceiling toward the downstairs bathroom, but whether there's a vent on it is anyone's guess). I shall have to get hubby up the ladder I think :D


    You know, I would absolutely love to do that! (it would have been solid fuel originally anyway, the Rayburn dates from the 1950s :D)

    Except for one big problem... the chimney into which the Rayburn currently vents (flues?) has a dog-leg (I guess that's what it's called) in it, and although we haven't found out for certain, we're assuming - what with regulations nowadays - that we wouldn't be 'allowed' to have smoke going up into that chimney (I would love to be proven wrong on that though!)

    To demonstrate what I mean (you must all know by know I love doing my little diagrams). Brace yourselves:

    This is the view looking at the Rayburn from inside the kitchen (I have no idea what this sort of chimney arrangement is all about (!) but it is what it is):
    upload_2019-10-12_19-22-59.png



    And this is the view from the outside wall:
    upload_2019-10-12_19-29-51.png

    We don't know the route from the door into the main chimney breast as we can't see that, but I'd guess it goes up diagonally to meet the main chimney?

    Anyway... a big no-no for solid fuel, or ok?
     
  15. Nige F

    Nige F

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    I'm not sure but a HETAS bod would know ;) about the current regs
     
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  16. Alec_t

    Alec_t

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    Could you disconnect the towel rail from the tank and use an inline heater in a loop with just the towel rail? There may be a suitable heater available off-the-shelf if you don't fancy the DIY approach shown in the video :).
     
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