Whirlpool Microwave Error Code F3.T4

The F3.T4 error code on a Whirlpool microwave indicates a magnetron thermistor failure. The magnetron thermistor is a temperature-sensing component mounted directly on or near the magnetron tube, which is the core component responsible for generating microwave energy. The thermistor monitors the magnetron's operating temperature and sends resistance-based signals to the control board. When the control board detects that the thermistor's signal is outside the expected range, whether due to an open circuit, short circuit, or implausible resistance reading, it sets the F3.T4 fault code and halts microwave operation to prevent potential overheating damage.

The most common triggers for this code include a failed thermistor, a loose or corroded connector at the thermistor harness, or damage to the wiring between the thermistor and the control board. Because the thermistor is located near the magnetron, which generates significant heat during operation, the connector and wiring insulation in this area are prone to heat-related degradation over time. A thermistor that has drifted out of its calibrated resistance range will also trigger this fault even if the physical connection appears intact.

Diagnosis should begin with the microwave fully unplugged from power, as the magnetron circuit retains high-voltage charge even after the unit is switched off. After confirming the power is disconnected and capacitors are discharged, inspect the thermistor's wiring harness connector for looseness, corrosion, or burnt contacts. If the connection is secure and undamaged, the thermistor itself should be tested with a multimeter and replaced if readings fall outside the specified range for the component.