AEG Washer Error Code E77

Error code E77 on an AEG washer indicates an open circuit condition in the NTC (Negative Temperature Coefficient) thermistor circuit. The NTC thermistor is a temperature-sensing resistor responsible for monitoring water temperature inside the drum during wash and rinse cycles. When the control board detects that the NTC circuit is open, meaning electrical continuity has been lost, it triggers E77 and typically halts the cycle to prevent operating at an unknown or uncontrolled temperature.

An open circuit in the NTC path can occur at several points: the thermistor itself may have failed internally, the wiring harness or connector between the thermistor and the control board may have a break, or the ribbon cable that carries signals between the main board and the interface or sensor assembly may be damaged or seated incorrectly. The ribbon cable is identified as the first diagnostic target, which suggests that connection failures at that cable are a frequent root cause of this fault in this model range.

Because the NTC thermistor changes resistance with temperature, a functioning sensor should show measurable resistance rather than an open line. A true open circuit, where resistance reads as infinite or out of range, points to either a broken thermistor element, a disconnected or corroded plug, or a break in the ribbon cable. Technicians should inspect the ribbon cable first for damage or poor seating before testing the thermistor resistance directly.