@burnsie did you have any Error faults come up when you installed yours? I installed the same one this afternoon hard wired to the Setec, it turns on okay and displays the temp and after 30-60 second it comes up with ERR and then flashes and the alarm goes off.
Hey @AzHaych thats not good news, my install seem to go fine no error codes etc, only problem I had with mine was that the unit is in two parts, and in order for it to work correctly the connection between the two needs to be sealed/connected tightly otherwise the display goes off and looses power from the back section where the wiring connects.
Mine also had the built in battery removed, so I assume yours only can be powered by the 12v as well? I know pressing the buttons a few times takes you through some different displays but sorry haven't seen the err message as yet.
Hopefully the guy comes back to you soon with a solution.....