Immersion thermostat change

Discussion in 'Electrics UK' started by JulianP, 11 Jul 2020.

  1. JulianP

    JulianP

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    Just a quick question.

    I've got a side entry immersion on an unvented tank There's actually two elements but just one in use as there's no E7. The immersion thermostat is of a type with spade terminals that push onto the heater element. I'm aware that a replacement must have an over temp trip, but are these thermostats all the same or manufacturer specific? I'm thinking that the dimensions may vary and not necessarily marry up to the orifice and heater terminals.

    Thanks.
     
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  3. Taylortwocities

    Taylortwocities

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    It depends on the make. Which unvented tank is it?
    Some tanks have an over temp cut out separate to the immersion itself.
     
  4. ericmark

    ericmark

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    I would not think they would be the same, as those which are used with alternative heating have reset button, but those which are the only control have non re-settable over temp, so if thermostat fails it must be changed, you would not want that if the solid fuel heating could trip the electric over temperature cut-out.
     
  5. Johnmdc

    Johnmdc

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    I take it that the thermostat is faulty if so then why not just use the thermostat out of the unused one?
     
    Last edited: 12 Jul 2020
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  6. JulianP

    JulianP

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    That is a good point, but they're about 10 years old and I have an idea that an electrician already did that some years ago so I would like a spare. It's for a tenanted property. The safety trip had tripped on it, I reset it easily enough but I'm no convinced if it won't trip again. Although someone had wound the normal adjustment to full hot so that won't help.
     
  7. JulianP

    JulianP

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    The OT is on the 'stat. Why would the tank manufacturer be of significance? Isn't the thread form for side entry immersion heaters the same for them all?
     
  8. Taylortwocities

    Taylortwocities

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    I ask because I had to replace a stat for a Megaflo unvented tank. It was a specific type and nothing like your regular immersion stat.

    Maybe it would be easier if I ask you the question in a different way:
    Is this a Megaflo tank?
     
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  9. flameport

    flameport

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    The thread might be, but there are different manufacturers of immersion heaters and thermostats. Some might be compatible, others not.
    All unvented cylinder immersion heaters have an over temperature cutout in them. That may be part of the thermostat, of it may be a separate device adjacent to the thermostat.

    If you need a new thermostat, get an identical one from the same manufacturer.
     
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  11. bernardgreen

    bernardgreen

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    As I recall it the immersion heater is required to have a safety over temperature cut out as part of the the thermostat in the immersion heater.
    This cut out has to be manually reset if it trips.

    It makes sense to have that cut out in the immersion thermostat rather than rely on the cylinder thermostat to shut the electric heater OFF.

    If the cylinder was empty then a faulty immersion thermostat could allow the immersion heater get red hot if there was no safety cut out.
     
  12. Taylortwocities

    Taylortwocities

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    Example. Megaflo stat.
    The spade connectors on the back push on to female contacts on the immersion housing.

    EE6FFC80-B609-42DD-B00B-C66A6951441C.jpeg
     
  13. JohnW2

    JohnW2

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    It appears that one can still get ones without an integral cut-out ...
    upload_2020-7-12_14-16-40.png

    It's always rather surprised me that the cut-outs are usually part of the thermostat, rather than separate and 'independent' (i.e. part of the element etc.). In the absence of any other source of heating, the cutout is presumably only relevant if the thermostat itself fails, and it if failed in some sort of catastrophic fashion, I would have thought that there would be a risk that an integral cut-out would also become non-functional.

    Kind Regards, John
     
  14. JulianP

    JulianP

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    Yes, that's the correct idea, it just pushes on to the heater contacts, a neat idea. But I do not know if I have a ''Megaflo'' 'stat as it's 70 miles away at the moment! This particular type of thermostat seems standard for side entry heaters, I'm still not sure if they are dimensionaly standard or not. The usual places all list these things and without trying it for size it's hard to say.
     
  15. JulianP

    JulianP

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    What I can tell you is this, having tested the thermostat with my multimeter: The regular contacts that cycle the power to maintain temperature break the connection between live supply and heater input. The overtemp trip contact breaks the supply from heater return to neutral. So in a way it is two separate units, just within the same unit.
     
  16. JohnW2

    JohnW2

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    Sure, one would obviously expect there to be two separate mechanisms but, as I said, and given that both are within close proximity in the same small space, I would have thought that it was not impossible that a 'catastrophic failure' (e.g. thermal damage) could probably disable both.

    Kind Regards, John
     
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