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  1. #1
    Join Date
    Mar 2018
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    UK
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    Mitsubishi Ecodan U4 Error



    Hi all,

    I have an 11 year old Mitsubishi Ecodan that is showing a U4 error code on the control panel. Ive looked up the error code:

    Open or close circuit Ecodan thermistors (TH3, TH32, TH33, TH6, TH7, TH8) open or close circuit or disconnected from main board.

    Does this require a straight swap out of the main power baord?

    Thanks in advance.



  2. #2
    Join Date
    Feb 2008
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    england
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    Re: Mitsubishi Ecodan U4 Error

    you probably need to replace one of the sensors check the discharge sensor first

  3. #3
    Join Date
    Mar 2018
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    Re: Mitsubishi Ecodan U4 Error

    Quote Originally Posted by martinw58 View Post
    you probably need to replace one of the sensors check the discharge sensor first
    i order a replacement power board which I switched out - didn't fix the issue. However after checking the thermistors for their resistance readings the pump spun up after reconnecting them to the board - the pump ran for 30 minutes long enough to heat the cylinder. Then an hour later I had the U4 error again. I left the machine for sometime, removed each thermistor form the board took the reading and again the pump spun up, this time for about 5 minutes but stopped when I was carefully removing the corner panel where the PCBs are.

    Whenever the pump stops I get good resistance readings, I'm wondering if it is an issue on the control board rather than the actual thermistors?

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