H1
Oster
Cavity overheat protection triggered
Microwave shows H1 and stops; often after extended cooking at high power.
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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
Blocked ventilation, Failed cavity thermal cutout, Overuse at high power without rest, Faulty cooling fan
How to Fix / Troubleshooting
Safety first: Unplug the microwave and allow it to cool.
- Cool-down period: Let the unit sit unplugged for at least 30–45 minutes, then plug back in and test. Overheat protection may reset.
- Check ventilation: Ensure there is at least several inches of clearance around the sides, back, and top. Remove any items blocking vents.
- Inspect cooling fan: During a test cook, listen for the fan. If it does not run, the fan motor or its wiring may be defective and should be replaced.
- If H1 recurs quickly: The cavity thermal cutout or related wiring may be failing. This requires disassembly and testing by a technician.
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Repair Difficulty
Hard
4/5
Required Part
Cavity Thermal Cutout
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