Thermistor overheat question

Discussion in 'General Electronics Chat' started by Presstotest, Apr 27, 2019.

  1. Presstotest

    Thread Starter New Member

    Apr 27, 2019
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    Hi,
    Looking for some help please for my new Japanese hydronic heat pump which keeps throwing up an E002 message, which in the booklet says “supply water side thermistor overheating”. Solutions in the manual are “check leakage of the system water, the blockage. If no problem, exchange control of the PCB or replace whole unit” (that is the translation from Japanese to English)

    Could someone please explain what it means and how I could fix it? For info the heat pump is used in the Japanese domestic market and parts of N America (I’m using it in southern Australia) and I’m using it on the low pump speed 8KWh mode to produce a maximum output water temp of 70C which is considered hot for hydronic heat pumps. Inlet (supply?) water is about 30-40C after it has been through the radiators in the house and back out through the buffer tank to cool the water as much as possible and create a high delta T for efficiency.

    Any help would be much appreciated - I’m a complete novice so go easy. I can get most info relating to the system including current it draws, system PSI, and inlet/outlet water temps.

    Thanks
     
  2. MisterBill2

    Distinguished Member

    Jan 23, 2018
    3,252
    635
    Based on no other information I offer a guess that perhaps an air pocket is forming around the thermister in question and resulting in it not being at the water temperature. The other guess is that there is a poor solder connection due to the use of lead free solder. I am also guessing that the device was actually produced in China by a Japanese company, because of the cheaper labor. It may also be that you are getting air into the water intake line because of a small leak, and since it is a suction line there is no dripping to disclose the leakage. But once again, these are guesses based on really not much information on your specific system.
     
  3. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
    7,650
    1,868
    Do you have any specification for the maximum water inlet temperature?
    Can you check the inlet temperature at which it shuts down and see if it is at a consistent temperature?
     
  4. drc_567

    AAC Fanatic!

    Dec 29, 2008
    639
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    ... Are you able to inspect the thermistor in some way? There may be debris or something that is shorting the two leads and sending a false value to the control board.
     
  5. bertus

    Administrator

    Apr 5, 2008
    19,523
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    Hello,

    Is the distance to the wall and the fence not to close?
    When there is no room for the air from the fan to get away, you can have a heat build up.
    What does the manual say about free space around the unit?

    Bertus
     
  6. MisterBill2

    Distinguished Member

    Jan 23, 2018
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    OK, it just occurred to me that the correct translation from Japanese to sensible speech is that the inlet water temperature is too high. So what you need is to connect the system to a source of cold well water for it to work as claimed. But if you lack a close by deep well there may be a problem,
     
  7. Presstotest

    Thread Starter New Member

    Apr 27, 2019
    2
    0
    Thanks everyone for their replies.

    Have followed up on Mister Bill’s comments about possible air pockets. Have bled the system and definitely got some air out of it. System seems to be running fine now, so that may have been the problem. Will have to wait and see over the next few days if error code appears again.

    Re the other posts, no max inlet water temp specified (have posted up machine specs) but am tending to think it may not be related to inlet water temp actually overheating as the inlet temp rarely gets above 35-40C and the error code has appeared when the system is completely cold and also when it has been running for several hours. Both these cases could suggest it was air related - I didn’t realise how sensitive these heat pumps were to air in the system (and water pressure).

    Plenty of space around the machine and also around the extract fan. Have also checked the inside of the machine and there is no debris present as it is brand new.

    Thanks again for help.

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  8. MisterBill2

    Distinguished Member

    Jan 23, 2018
    3,252
    635
    Air pockets in fluid systems are often the cause of an assortment of problems. And I learned several years ago that on some systems it is not possible to recirculate the cooling water. That was an expensive lesson, too!
     
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