F4
Emerson
Cavity or Magnetron Thermal Cutout Open
Microwave shows F4 and stops heating; fan and light may still operate.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Open cavity thermal fuse, Open magnetron thermal fuse, Overheating due to blocked vents, Failed thermostat
How to Fix / Troubleshooting
Safety first: Unplug the microwave and allow it to cool.
Ventilation:
- Ensure vents are clear and filters are clean.
Check thermal fuses:
- Remove the outer cabinet and locate thermal fuses/thermostats on the cavity and magnetron.
- With wires removed, test each fuse for continuity. Any fuse that tests open must be replaced with the exact Emerson-specified part.
- Investigate and correct the cause of overheating (blocked vents, failed fan) before replacing fuses.
Warning: Do not bypass or jumper thermal fuses; this is a serious fire and safety hazard.
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Repair Difficulty
Hard
4/5
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