Hi
I think @lxonline has this one exactly.
Sometimes the pins on the temperature probes are not long enough to reach the terminal connections on the GX device (though they are long enough to reach the multiplus terminal connections).
I have had this exactly situation before.
You can quickly tell because when you insert the temp probe connections into the GX terminal block it should not be possible to pull them back out again (with any reasonable amount of force). Instead you should only be able to remove them by pushing on the orange tab.
If you can remove them, they aren’t getting in far enough.
The quick work around is to remove the crimped ends, and just strip back the wire so that it’s long enough and insert that. You will need to twist the end, and ideally be careful with the insertion because it will be weaker. But it’s quite safe, there is no voltage on these connections it’s just reading resistance.
You can see here two identical model temperature probes supplied by Victron, one has a longer connection area than the other. Only one properly connects to the GX device.
