What F3T4 Means
JennAir's F3T4 page names the magnetron temperature thermistor or the associated wiring. The magnetron is the part that actually generates microwave energy, and this sensor is the thermal protection watching it.
Common Causes of F3T4
- A magnetron thermistor that has failed
- A cooling fan no longer keeping the magnetron within temperature
- A break in the thermistor wiring
🔧 One Safe Check You Can Try
Stop using the microwave and switch it off at the breaker. This is the one sensor in the appliance whose whole purpose is to protect the highest-energy part, and JennAir's page offers only a reset beyond that.
⚠ Why You Shouldn't Go Further Than That
- The magnetron area contains the high-voltage capacitor and transformer, which between them hold enough stored energy to be lethal after the unit is unplugged.
- A thermal sensor problem can mask a genuine cooling problem, and a magnetron allowed to run hot is both an expensive failure and a safety one.
- Replacing the sensor without establishing whether the magnetron was actually overheating leaves the underlying cause in place.
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.
Technical Reference
- Code
- F3T4
- Appliance
- JennAir microwave
- Maker documentation
- JennAir owner manuals and use & care guides
- Checked
- September 2026
Code meanings can change between control generations. Before acting on a code, match the full model number on your appliance's rating label against the manual for that model. We are an independent repair service, not affiliated with Whirlpool Corporation.