[oldtimer]

I went today to change the transformer and obviously it didn't solved the problem. I pushed the button on the contactor and there is no continuity between L1 and T1. I guess the contactor is out.

Did the contactor close ?

If it did and you have contact between L2 and T2 and L3 and T3 .

Then obviously one pole is not making !

Check your overloads !