With reference to the jpg Ascoli65 posted above...
The voltage changes from 67v to 49v yet the current increases from 1.8A to 2.4A.
That can only happen if the impedance of the load (the heating coil) changes. So something is up whatever the cause.
I think the voltages may have been switched?
Let's calculate the coil resistance assuming they were switched...
67v/2.4A = 27.9 Ohms
49v/1.8A = 27.2 Ohms
Close enough to suggest this might be the cause?
I haven't looked to see if we know the coil resistance.