Pipe thermostat for hot water immersion heater - would it work?

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loyalstokie
loyalstokie Posts: 53 Forumite
in In my home (includes DIY) MoneySaving
Our hot water comes from a hot water tank and immersion heater.

The immersion heater is set to the right temperature (65 degrees/minimum if I remember correctly), but gets ridiculously hot if left on for a long time e.g. overnight.

As it is difficult to access the immersion heater, could putting a pipe thermostat into the circuit solve or help the problem?

Where would be the best place to attach it? - I'm thinking somewhere along the hot water pipe out (or cold in if I can get to it!).

As the immersion heater a a resistive current, I don't see a problem there.



Unless I'm missing something it seems like a easy solution.

Any thoughts?
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  • jk0
    jk0 Posts: 3,479 Forumite
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    Sounds to me like you need a new thermostat, set a bit lower.
  • Owain_Moneysaver
    Owain_Moneysaver Posts: 11,357 Forumite
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    A central heating pipe thermostat won't be rated to cope with the heavier current of the immersion heater.

    Also, it would only sense the temperature in the pipe, not in the hot water cylinder.
    A kind word lasts a minute, a skelped erse is sair for a day.
  • southcoastrgi
    southcoastrgi Posts: 6,298 Forumite
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    Just replace the stat in the immersion & set it to the correct temp of 60°
    I'm only here while I wait for Corrie to start.

    You get no BS from me & if I think you are wrong I WILL tell you.
  • loyalstokie
    loyalstokie Posts: 53 Forumite
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    jk0 wrote: »
    Sounds to me like you need a new thermostat, set a bit lower.
    southcoastrgi wrote: »
    Just replace the stat in the immersion & set it to the correct temp of 60°
    It could be set at 60° - I'm quite sure it was set at the minimum when I checked.


    Owain_Moneysaver wrote: »
    A central heating pipe thermostat won't be rated to cope with the heavier current of the immersion heater.
    The one I was looking at has a switching current of 16A resistive

    Owain_Moneysaver wrote: »
    Also, it would only sense the temperature in the pipe, not in the hot water cylinder.
    I just want it to turn off before it reaches a temperature where I can scald myself.



    The thermostat does work, but at a much higher temperature. I have a feeling that the thermostat could be covered in limescale and need cleaning or replacing (which could take me all day or leave us without hot water).



    Is there any way to test the thermostat?
  • Mutton_Geoff
    Mutton_Geoff Posts: 3,820 Forumite
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    loyalstokie wrote: »
    I just want it to turn off before it reaches a temperature where I can scald myself.

    The thermostat does work, but at a much higher temperature. I have a feeling that the thermostat could be covered in limescale and need cleaning or replacing (which could take me all day or leave us without hot water).

    Is there any way to test the thermostat?


    The pipe stat won't sense the hot water until it flows through the pipe by which time, it's too hot to do anything about.


    Your stat clearly isn't working properly. Why not just replace it and fix the problem rather than the symptom?
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  • ohreally
    ohreally Posts: 7,525 Forumite
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    loyalstokie wrote: »
    The thermostat does work, but at a much higher temperature.

    The 'stat has clearly failed, change it, job done.
    Don’t be a can’t, be a can.
  • coffeehound
    coffeehound Posts: 5,674 Forumite
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    loyalstokie wrote: »
    I have a feeling that the thermostat could be covered in limescale and need cleaning or replacing (which could take me all day or leave us without hot water).

    Is there any way to test the thermostat?

    You don't need to drain down the cylinder to change the t-stat; it slides into a pocket in the heater. You could probably test it with a multimeter, a thermometer, and a pan of hot water, but it would probably easier to just replace it :)
  • Mutton_Geoff
    Mutton_Geoff Posts: 3,820 Forumite
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    edited 15 October 2019 at 9:45AM
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    ohreally wrote: »
    The 'stat has clearly failed, change it, job done.

    Agreed, they usually come in three sizes. Take the old one out, measure it and buy a replacement for around a tenner. Check whether your old one has a cut out or not.

    And if you don't know what you're doing, call an electrician.

    https://www.tlc-direct.co.uk/Main_Index/Water_Heating_Index/Immersion_Heaters_2/index.html#Immersion_Heater_Stats


    Question for the OP, is the electric immersion heater your only source of hot water or is it a hot water cylinder fed by your gas boiler and a back up electric immersion heater?


    If the former then it will be the cylinder stat (strapped to the side with a length of net curtain wire) that needs adjusting/changing, not the immersion stat if the water is too hot when supplied by the boiler.
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  • loyalstokie
    loyalstokie Posts: 53 Forumite
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    coffeehound wrote: »
    You could probably test it with a multimeter, a thermometer, and a pan of hot water, but it would probably easier to just replace it :)
    I might give that a go - it would involve taking a shelf or two out of the airing cupboard

    Mutton_Geoff wrote: »
    Question for the OP, is the electric immersion heater your only source of hot water or is it a hot water cylinder fed by your gas boiler and a back up electric immersion heater?
    There is a oil boiler and wood burner which both go to a neutraliser. It heats the hot water by convection and there is a valve between the hot water tank and neutraliser which closes when the heating is turned on - no pipe or cylinder stat on the boiler side.

    Page 5 of might help https://solidfuel.co.uk/pdfs/central-heating-link-up.pdf
  • loyalstokie
    loyalstokie Posts: 53 Forumite
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    Well that seemed scare you off!



    Update: After twiddling the thermostat backwards and forwards a bit it is now working (maybe a freed something), but seems more accurate the longer it is left on.

    I have now read that a immersion heather thermostat can be set at 50 degrees, rather than the 60 degrees I had previously found - so I will change that.



    I have read plenty about whether to leave an immersion heater on all the time, have it on a timer or on when needed (and risk forgetting to turn it off!)

    Question: Is it possible that when heating from cold will (depending where the thermostat is) the temperature reach above what the thermostat is set at before turning off it tries to heat the cold water at the bottom? (I have an 18" thermostat).
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