LG GWL227HBQA – Overheated at defrost

Hi all

I have been asked to look at this fridge freezer as it had lost temperature, when I examined it I found that the evaporator was clear but there was a very large ball of ice above it, you will also see in the pictures that it looks like it has overheated when defrosting and melted the plastic back panel. I have tested all the sensors, heater and thermal fuse and everything measures okay (I don’t know what value the sensors should be but the fridge and freezer ones match values), I have also insulation tested the unit and found no issue. The defrost relay on the control board appears to be working correctly.

I suspect that the defrost sensor may be dropping out so would like to change it – does anyone know the part no? (Also part no for the back panel)

Is there any other known issue that would cause this sort of damage to the back panel?

I have de-iced it and left the defrost heater disconnected for a couple of days while I find more information because I am not sure what would have caused this.

I would welcome your thoughts/advice on what else you would be looking for

Thank you

Jem