Microwave High Severity
F1 Appliance Error Code

Whirlpool Microwave F1 Error: Cavity thermistor open

If you are dealing with a whirlpool microwave f1 error, this guide will help you understand the cause and find the right solution quickly. What Does Microwave Error Code F1 Mean? Error code F1 on Whirlpool WMH, WMC, and WML series microwaves indicates that the oven cavity thermistor has an open circuit or is reading […]

By Lucy Senior Whirlpool Appliance Technician

Some Steps

DIY Fixable

from $140

Typical Repair Cost

1-2 hours

Pro Repair Time

Quick Assessment

Answer to continue safely

Is it safe to keep using?

No. The microwave cannot heat food safely with F1 active. The magnetron is disabled. Do not attempt to use the microwave for cooking until F1 is resolved.

Can I reset the code?

No. A hard reset clears F1 from the display, but the code returns immediately on the next cook attempt if the thermistor or wiring fault is still present.

When to stop immediately?

Stop if you notice: Stop all troubleshooting if you have opened or are considering opening the microwave outer cabinet — internal components carry lethal voltage., Stop if F1 returns immediately after every hard reset and the external connector is secure — internal board or thermistor replacement is required..

Symptoms You May Notice

Microwave stops heating after a few seconds of operation

The magnetron starts briefly but the board cuts power to the heating circuit within seconds of detecting no valid temperature feedback from the cavity.

Cooking timer counts down but food remains cold

The display shows the cook cycle progressing normally, but the magnetron is not energizing because the thermistor fault has disabled the heating relay.

F1 appears at the start of every cook cycle

The error is displayed consistently at the beginning of each cooking attempt, before significant heat could have accumulated in the cavity.

Turntable and light work but no heat is produced

The turntable motor and interior light function normally, confirming the control board and low-voltage systems are operational — only the heating circuit is disabled.

Possible Causes

1

Open thermistor or disconnected harness

The thermistor element has failed open internally, or its wiring plug has separated from the control board input, presenting infinite resistance to the board.

DIY Possible
2

Corroded thermistor connector pins

Steam and food vapor inside the cavity accelerate corrosion on the thin thermistor connector pins, increasing contact resistance until the board reads an open circuit.

DIY Possible
3

Defective control board thermistor circuit

A failed pull-up resistor or ADC input on the control board can falsely report an open thermistor even when the sensor itself is functioning correctly.

Requires Professional

Safe Checks You Can Do

These checks are safe for homeowners. No disassembly required. Do not remove panels or access internal components.
  1. 1

    Perform a hard reset

    Unplug the microwave from the wall outlet completely. Wait 60 seconds to allow the control board to fully discharge, then plug it back in and test a short cook cycle.

    Always unplug at the wall outlet — do not rely on the microwave door switch or a power strip to isolate the appliance for safety purposes.

  2. 2

    Inspect the thermistor wiring connector

    With the microwave completely unplugged and waiting 2 minutes after unplugging to allow capacitor discharge, access the thermistor connector (usually visible through the vent grille without full disassembly on countertop WMC models). Unplug and firmly re-seat the connector.

    Never open the microwave outer cabinet or touch any internal components — the high-voltage capacitor can hold over 2,000 V and is lethal even minutes after unplugging.

  3. 3

    Clean around the thermistor connector

    With the unit unplugged, use a dry cotton swab to gently remove any food residue or moisture from the connector area. Allow to dry fully before reconnecting power.

    Do not spray any liquid cleaner inside the cavity near the thermistor — even small amounts of moisture in the connector can cause intermittent F1 faults.

When to Call a Professional

Contact a qualified technician if:

  • F1 returns after a hard reset and the thermistor connector is confirmed securely seated with no visible damage.
  • Thermistor resistance measured at the connector reads open (infinite ohms) at room temperature — thermistor replacement required.

Need Professional Help?

Find qualified technicians in your area for proper diagnostics and repair.

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