Monogram Microwave F3 Error: Humidity sensor fault
The F3 error code indicates that the humidity or moisture sensor inside the microwave cavity is producing a reading outside its expected operating range. This sensor is used by auto-cook and sensor-cook functions to detect steam released by food; a fault prevents the sensor circuit from operating correctly.
~20%
DIY Fixable
From $150
Typical Repair Cost
1–2 hrs
Pro Repair Time
Quick Assessment
Answer to continue safely
Is it safe to keep using?
Maybe. Manual timed cooking modes are safe to use while the F3 fault is present. Sensor-based cooking modes should be avoided until the sensor is repaired, as they will not function correctly.
Can I reset the code?
Yes. A 60-second power-cycle combined with cavity drying may resolve F3 if moisture contamination was the cause. If the sensor itself has failed, a reset will not permanently clear the code.
When to stop immediately?
Stop if you notice: Stop using sensor-cook modes immediately — these will not operate correctly and may under-cook or over-cook food., Stop all use if F3 appears even during manual timed cooking cycles, as this could indicate a broader control board fault..
Symptoms You May Notice
Auto-cook or sensor-cook functions fail to start
The microwave refuses to begin any cooking cycle that relies on sensor input, such as "Sensor Cook" or "Auto Reheat," displaying F3 instead.
F3 displayed at the start of a sensor-cook cycle
The error appears immediately when a sensor-based cook mode is selected, indicating the control board cannot obtain a valid reading from the humidity sensor.
Manual cook modes still function normally
Standard timed cooking at a set power level continues to work, because manual modes bypass the humidity sensor entirely.
Condensation visible on interior cavity surfaces
Excess residual moisture in the cavity from prior cooking may cause erratic sensor readings and trigger F3 if the sensor cannot establish a valid baseline.
Possible Causes
Moisture or food residue on the sensor
Splattered food or condensed steam can coat the humidity sensor element, causing a continuously high or out-of-range reading that the control board interprets as a fault.
DIY PossibleFailed humidity sensor
The sensor element itself can fail open or short due to age, heat cycling, or contamination, requiring replacement of the sensor assembly.
Requires ProfessionalWiring harness fault between sensor and control board
A broken, corroded, or loose connector in the wiring harness between the humidity sensor and the main PCB can mimic a sensor failure.
Requires ProfessionalSafe Checks You Can Do
-
1
Power-cycle and allow cavity to dry
Unplug the microwave for 60 seconds. Leave the door open for 15–20 minutes to allow any residual moisture inside the cavity to evaporate, then restore power.
Running the microwave empty on a low-power timed setting for 30 seconds can help evaporate residual moisture before retrying a sensor-cook mode.
-
2
Clean the cavity interior thoroughly
With the unit unplugged, wipe down all interior surfaces — ceiling, walls, floor, and turntable — using a damp cloth and mild detergent. Pay special attention to the area directly above the turntable where the sensor is typically located.
Avoid abrasive pads on the cavity coating. A paste of baking soda and water removes stubborn food deposits without damaging the interior finish.
-
3
Test manual cook mode
Restore power and run a 1-minute timed cook cycle at 100% power with a cup of water. If this completes without error, only sensor modes are affected and F3 is likely a sensor or wiring issue.
Confirming manual modes work narrows the fault to the sensor circuit specifically, which helps when communicating with a technician.
When to Call a Professional
Contact a qualified technician if:
- The F3 code persists after thorough cavity cleaning and multiple power-cycles, indicating a failed sensor or wiring fault.
- The humidity sensor connector or wiring harness shows visible corrosion, burn marks, or physical damage.
- F3 appears during standard timed cook cycles, suggesting the control board rather than the sensor alone may be at fault.
Need Professional Help?
Find qualified technicians in your area for proper diagnostics and repair.
Microwave Repair Service Schedule Appointment