H3
Oster
Magnetron overheat protection triggered
Microwave shows H3 and shuts down during operation; may restart after cooling.
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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
Failed or weak cooling fan, Blocked air intake or exhaust, Magnetron running at high duty cycle for extended time, Dust buildup on cooling passages
How to Fix / Troubleshooting
Safety first: Unplug the microwave and let it cool.
- Allow cool-down: Wait 30–60 minutes before attempting to use the microwave again.
- Clean vents: Use a vacuum or soft brush to remove dust from intake and exhaust vents. Ensure adequate clearance around the unit.
- Check fan operation: During a short cook test, listen for the cooling fan. If it is noisy, slow, or not running, the fan motor may need replacement.
- If H3 repeats: The magnetron may be overheating due to internal failure. Continued use can be unsafe; have the unit inspected by a professional.
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Repair Difficulty
Hard
4/5
Required Part
Cooling Fan Motor
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