GE Microwave F1 Error Code: Open Thermal Sensor (Cavity Thermistor)

What the code means

GE's support article "Microwave - Error, Fault or Function Codes", which lists the fault codes built into its microwave controls for technicians, defines F1 as an open thermal sensor, due to excessive heat in the microwave cavity, and F2 as a shorted thermal sensor. GE's 240-volt Advantium list also gives F1 as an open thermal sensor. GE's Technical Service Guide 31-9177 for the 120-volt Advantium (PSB1200, PSB1201, ZSC1201, ZSC1202) explains that when the control detects a failure it stops cooking, beeps four times and shows the code. For F1 it says the control watches for both an open thermistor and a change in oven temperature: if the oven temperature hasn't risen enough within a set time, F1 can appear even though the thermistor is fine, so a technician checks the thermistor's resistance first, then looks for heaters that aren't working or a large load of cold food. Not every GE microwave has an oven heater, so on a plain microwave F1 points mostly to the sensor, its wiring and the control. GE says shutting off the breaker or fuse for 30 seconds sometimes clears a fault code, but some cases need service. F1 is not the same as F3 (shorted touch pad), F4 or F5 (humidity sensor) or PF (a power failure occurred).

Likely causes

• The cavity thermal sensor (thermistor) has failed open, or its plug or wires have come loose or been heat-damaged (GE fault code list; GE Technical Service Guide 31-9177)
• Excessive heat in the cavity, for example blocked vents or a long cooking run (GE fault code list)
• On convection and Advantium models: the oven didn't warm up as fast as the control expected, because of a large cold load or a convection heater that isn't working (GE Technical Service Guide 31-9177)
• Less often, the control board's sensor input, once the sensor and wiring check out

Safe DIY checks

1. Press Clear/Off or Cancel to clear the code, then try the cooking function again. GE's Advantium instructions say to do this first.
2. If F1 comes back, switch off the breaker or remove the fuse that feeds the microwave for 30 seconds, then turn it back on. GE says this sometimes clears a fault code.
3. Make sure nothing is blocking the vents, and on an over-the-range model check that the vent grille and filters aren't packed with grease. Let the microwave cool down fully before trying again.
4. If F1 only appeared while you were cooking a big frozen or fridge-cold item in a convection or speed-cook mode, try a smaller load. GE's service guide says a large cold load can trigger F1 even when the sensor is fine.
5. Stop there if F1 keeps coming back. The sensor and its wiring sit inside the case, and a microwave stores dangerous high voltage even when unplugged, so the remaining checks are for a technician.

Parts that commonly fix it

Always match the part number to your exact model.

Related codes

• F3 GE Microwave F3
• F4 GE Microwave F4
• FOOD GE Microwave FOOD
• LOC GE Microwave LOC
• PF GE Microwave PF

All GE codes →

Sources

1. GE Appliances: Microwave - Error, Fault or Function Codes (F1: open thermal sensor, due to excessive heat in microwave cavity; F2: shorted thermal sensor; 30-second breaker reset sometimes clears a code, some cases need service)
2. GE Appliances: Advantium 240 Volt - Error, Fault or Function Codes (F1: open thermal sensor; press Clear/Off, then 30-second power disconnect)
3. GE Technical Service Guide 31-9177, Advantium Oven PSB1200/PSB1201/ZSC1201/ZSC1202 (fault codes: cooking stops, 4 beeps; F1 oven cavity thermistor open, or oven temperature not rising in time; check thermistor resistance, heaters, large cold load)
4. AppliancePartsPros: F1 error on a GE microwave, a troubleshooting guide (check ventilation, sensor, wiring, then control board)