Hotpoint MBL2011CS freezer defrost heater stopped working

Dear sir,
I have a fridge freezer MODEL MBL2011CS, this on it's freezer side the DEFROST HEATER HAS STOPPED DEFREEZING THE ICE, every time my evaporator will get stocked with ice thereby reducing the coldness.
I am a fridge technician, I want to understand how the DEFROST HEATER is connected here, there are six pots, four wires from the sensor (2yellow and 2blue) and 2 white wires to the heater itself.
Thanks in advance.