H99
Hotpoint
Overheating or Magnetron Protection Fault
Microwave stops heating and shows H99; may occur intermittently under heavy use.
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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
Overheated magnetron, Blocked cooling vents, Failed cavity or magnetron thermal cut-out (TCO), Cooling fan not running, Inverter thermal protection triggered
How to Fix / Troubleshooting
Safety first: Unplug the microwave before inspection.
- Allow cooling: Let the microwave sit unplugged for at least 30 minutes to cool down fully, then reconnect and test.
- Check ventilation: Ensure there is adequate clearance around the microwave per the Hotpoint installation manual. Clear any obstructions from intake and exhaust vents.
- Inspect cooling fan: Remove the outer cabinet and verify the cooling fan motor spins freely and is not obstructed by debris.
- Check thermal cut-outs: Locate the magnetron thermal cut-out and cavity thermal cut-out (small disc thermostats). Ensure they are firmly attached and wiring is intact.
- Replace faulty components: If a thermal cut-out is open (requires meter to confirm) or the fan motor is seized, replace the defective part.
- Professional diagnosis: If H99 persists, the magnetron or inverter may be overheating internally and should be evaluated by a technician.
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Repair Difficulty
Hard
4/5
Required Part
Magnetron Thermal Cut-Out (TCO)
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