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Cylinder Heating Elements

Discussion in 'Plumbing and Central Heating' started by PrenticeBoyofDerry, 29 Jul 2019.

  1. PrenticeBoyofDerry

    PrenticeBoyofDerry

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    Could someone please explain why two elements would be linked across each other?

    Heating element (immersion) Backer BT 15/11 and BT11 1563814336595.jpg 1563814336429.jpg
     
  2. stem

    stem

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    Probably they are both the same unit, but maybe one is newer than the other. The 11 refers to the length of the rod in inches, and 15 is the current rating in amps.

    I can't think of any reason why there would be two wired in series, but surely both thermostat rods can't fit in the same thermowell, can they? Or has one stat had its rod removed?

    They don't appear to have a visible a 'cut-out' button on them either, so I would assume that this is the type of thermostat that should be used with a separate 'cut-out' something like this:

    Immersion.png
    Is it possible that the second thermostat has had its rod removed and then been wired in where the reset button should be?
     
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  3. AdvanceHelpline

    AdvanceHelpline

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    One is a control thermostat to set temp, one is a safety high limit thermostat
     
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  4. PrenticeBoyofDerry

    PrenticeBoyofDerry

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    I thought as much.
     
  5. PrenticeBoyofDerry

    PrenticeBoyofDerry

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    They both have rods attached and the cylinder allows both to enter the cylinder housing well. This occurs twice on the cylinder a set of two at the bottom then a set of two a third way up. This set uo allows for boost facility. Just never come across them being linked/paired like this. My assumption was one for heating and one for cut-out. Puzzling as the apartments are quite new.
     
  6. stem

    stem

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    Agreed, it's not something I've seen before. Normally the high limit stat has factory set preset operating temperature and has to be manually reset by pushing a button. Then, if after being reset it trips again it flags up that there is a fault with the main stat not switching off, and a repair is required.

    In your case these both just look like standard BT11 stats with an adjustable temperature range, so if one stat failed in a permanently closed position, I would imagine that the other would switch 'on' and 'off' and function as a normal thermostat and meaning no remedial investigation occurs. Until the second one failed too, possibly creating a dangerous condition.....Hmmm..

    I have just had a look on the Backer website and for the BT11" 15 amp Immersion Thermostat, it does say that it should be used with a Manual Button Cut-Out Part No 13115


    high limit.JPG

    This is the only cut out device shown on their website. However, as you say the immersion heater has two thermowells, it does suggest one is for a high limit thermostat. Perhaps the manufacturer of the actual immersion heater itself, might be able to provide some insight.

    I suspect that maybe two standard thermostats have been fitted, rather than one thermostat and a manually reset cut out.
     
    Last edited: 30 Jul 2019
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