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Immersion heater stat testing

Discussion in 'Electrics UK' started by Custom45, 17 Feb 2020.

  1. Custom45

    Custom45

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    Hi
    Searched forums but couldn't find an answer to what is probably a common question..

    Immersion heater appears to have packed up, no hot water last night or today. The light on the timer switch comes on when the timer kicks in or when you manually boost it, but no hot water.

    Either the element has packed up or possible just the thermostat has failed? Is there a way of testing the thermostat to find out if it's a faulty stat or a faulty element? Its a much easier job putting a new stat in, rather than replacing whole unit.
     
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  3. oldbutnotdead

    oldbutnotdead

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    Visual inspection first- isolate supply, remove cap on back of heater, look for charred or failed cables or connectors.

    Then Multimeter. Isolate supply, remove cap on back of immersion heater. You'll see the live wire (red or brown) and a tail from the heater going into the back of the thermostat. Set meter to impedance Ω low range, check it is working (short probes, reading should go to zero), apply probes to those bare conductors. 0 reading is good, ∞ is bad.
    Next test- probes onto each tail of the heater, again ∞ bad, 20 ish good.
     
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  4. Custom45

    Custom45

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    Thanks very much. Will do this when I get home in a couple of days.

    Just to clarify, correct setting for my multimeter?

    15819298170806787255892773773593.jpg
     
    Last edited: 17 Feb 2020
  5. oldbutnotdead

    oldbutnotdead

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    Yeah that's the setting. Short the probes together & display should show zero
     
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  6. crystal ball

    crystal ball

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    Also check the overheat cut out if there is one, hard to spot on some stats, tiny pop up jobbie, reset with a small driver or a pen
     
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  7. oldbutnotdead

    oldbutnotdead

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    Ooh good point, forgot about that :)
     
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  8. Chris_W

    Chris_W

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    Sorry to jump on this thread, but I have a very similar issue. I checked voltage between L and N 230Vac (used my 2 pole voltage tester). Checked the resistance and it displayed OL (which I know is open loop/line). Checked the resistance between elements and got approx 21.3. I also checked for the reset.

    My question is (and relevant to OP): Can any make of thermostat be fitted providing it’s the same length, or does it have to be brand specific?

    I also checked voltage between L and thermostat tail and got 230vac?

    OP - There’s also a cracking video by John Ward:

     
    Last edited: 17 Feb 2020
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  9. Custom45

    Custom45

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    Thanks, yes will check the reset button, I think it has one. What would cause the button to trip though? If it is that is it a cause for concern?

    The Novice.. I may be wrong, but I think they're all interchangeable? I suspect if you got one from say screwfix then it'd fit yours fine, just get correct length. Will check the video.. cheers.
     
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  11. terryplumb

    terryplumb

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    Any brand will be ok ,but length has to be the same .
     
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  12. EFLImpudence

    EFLImpudence

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    Ok.

    If you mean the resistance across the thermostat contacts then it is open.
    If it is set to high then it is not working.

    If you mean between the ends of the element then it would seem to be alright.
    Slightly higher than would be expected; did you deduct the resistance of the leads?

    They are all the same.

    Indicates again that thermostat is open and element is alright.
     
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  13. terryplumb

    terryplumb

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    The oh stat trips when the thermostat fails ,and element heats continuously.
     
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  14. crystal ball

    crystal ball

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    I get quite a few calls to tripped stats, is usually a one off nuisance trip, turn the temp down a smidge
     
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  15. Custom45

    Custom45

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    Hmm.. been meaning to do that, hot water coming out really has been hot. Like scald your hand hot. I think it's set on either 65 or 70. Perhaps it has overheated & triggered the reset.
     
  16. Chris_W

    Chris_W

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    Didn't deduct lead resistance, but when I checked again it came in slightly lower approx 19.3? Maybe because it's auto ranging or dirty contacts? Yes I checked across thermostat contacts. Need to get a new one. Thanks.
     
  17. Custom45

    Custom45

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    Got my wife to check the stat last night, she said reset button had popped up, so pressed it in and it started working again. However this morning no hot water again and reset hasn't tripped this time. Not home for a little while yet so not yet tested with a meter.
     
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