I just realized we are all going down the wrong path.
6.9 KW total heater output = 2.3 KW per phase
2.3 KW per phase / 230 V phase to neutral / earth = 10 A
Measured current ~ 10 A.
Element resistance when hot, is around 23 ohms.
Top element is open, middle element is fine, bottom element is either opened or unpowered. Somewhere along the common connections is grounded. Probably at the top heating element, near the common connection point.
Agree! Without the calculations, I think that's what I suggested at first.
Whatever, I think you can safely say you need some new heater elements.
