Mitsubishi Ecodan U4 Error

[spacebiscu]

Hi all,

I have an 11 year old Mitsubishi Ecodan that is showing a U4 error code on the control panel. I’ve 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.

[martinw58]

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

[spacebiscu]

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?