Whirlpool Microwave Error Code F3.T1

The F3.T1 error code on a Whirlpool microwave indicates a thermistor failure on the UIB (user interface board). The thermistor is a temperature-sensing resistor embedded in or connected to the UIB that monitors the board's operating temperature. When the microwave's relay control board cannot read a valid signal from this thermistor, it registers the fault and displays F3.T1. The communication path between the UIB and the relay control board runs through connector P2 on the UIB side and connector P64 on the relay control board side.

The failure can originate from several points in the circuit. A loose, corroded, or damaged connector at P2 or P64 can interrupt the thermistor signal entirely, causing the control board to interpret the open circuit as a sensor fault. The thermistor itself may have drifted out of its acceptable resistance range due to heat damage, age, or physical damage to the sensing element. Wiring harness damage between the two boards, such as pinched wires or broken conductors, can produce the same result.

Because this fault involves temperature sensing on the user interface board, the microwave will typically disable heating functions as a safety precaution. Diagnosis should always begin with the power disconnected. Inspecting and reseating the P2-to-P64 connector harness is the first step, as loose connections are a frequent and easily corrected cause. If the connectors are secure and undamaged, resistance testing of the UIB thermistor and continuity testing of the wiring harness are the next appropriate steps before replacing any components.