What F3H Means
KitchenAid publishes F3H for two microwave families and names a slightly different part on each, so both are given here rather than merged. Built-In Microwave, including the microwave-oven combination: "There may be a problem with the Microwave Humidity Sensor, or the associated wiring." Over-the-Range Microwave: "There may be a problem with the Humidity Thermistor or the associated wiring." Both concern the component that watches steam coming off food so that sensor-driven cooking programs can decide when the food is done, but the names are not interchangeable and KitchenAid keeps them apart, so this page does too.
Common Causes of F3H
- A humidity sensor or thermistor fouled with cooking residue, or failed
- Wiring between that sensor and the board reading it
- A control channel no longer interpreting the sensor correctly
🔧 One Safe Check You Can Try
Let the appliance cool, and on an over-the-range unit switch off and cool the cooking surface below before standing at it. Cut power at the breaker for a minute, restore it, and watch the appliance for a minute. In the meantime use timed cooking rather than the sensor programs - the sensor is what F3H concerns and timed cooking does not use it.
⚠ Why You Shouldn't Go Further Than That
- The sensor sits in the vent path inside the cabinet, so cleaning or checking it means opening the appliance rather than reaching into the cavity.
- A microwave stores energy in its high-voltage capacitor, and that charge does not drain when the power goes off; opening the outer case is therefore dangerous even on a unit that has been disconnected for hours.
- Getting inside an over-the-range microwave means unbolting it from the cabinet above and lifting it clear of the range below, which needs two people and a clear cooktop before anything else.
Opening a panel to inspect or repair something yourself doesn't automatically cancel your manufacturer's warranty — but it can risk accidental damage, and some manufacturers do have specific service conditions. Check your product's warranty terms, or ask us, before deciding.