On 17/12/2019 14:46, Graham. wrote:
Help me out here. I thought I knew how a door interlock works and I
suppose the PTC thermistor could overheat and cause a fire, but I
can't see how the load of the main heating element influences it.
Does anyone know what the actual mode of faliure is?

Sounds like all the power, including the heater, goes through the door
interlock switch contacts and they probably can't cope with the current.

Big Clive gas a good teardown and explanation of a typical Indesit door
interlock at https://youtu.be/PIm7q_U3UEM