Probable heat probe malfunction, how do I test it?
It appears to be a contact resistance failure of the 1/4&quot; Quick Disconnect type plug causing a temperature exceeding the hotplate to melt the plastic.

The plastic used must withstand the thermal protection switch temperature and then some just as the PVC of the wire , which appears to be in tact.
When this contact loosens from vibration and increases it's contact resistance sufficiently at the heater current to cause a temperature rise, oxidation process increases and at some point resulted in a thermal runaway that caused failure.
The solution requires a very low resistance wire crimp to be made which requires a tool and some skill to ensure either wire or wire + insulation crimp is made so that the contact is gas tight.
Find a technician who knows how to crimp these very common equivalent plugs. The exact same is unlikely to find easily with this plastic at right angle.
however one can replace it with 
The wire must pass a 5 pound (&gt;2kg) pull test from the connector to ensure a reliable connection.  The plug must fit tight on the thermal switch.  If the vertical orientation is a problem, it may be pre-bent with care.