Microwave displays F8 and may shut down or refuse to start, sometimes after extended cooking.

Safety first: Disconnect power. Microwaves contain high-voltage components; do not touch the magnetron or capacitor.

Ventilation check:

• Ensure that the upper and rear vents are not blocked by cabinets, wall coverings, or debris.
• Clean any grease filters and exterior vents.

Fan operation test:

• Restore power and start a short cook cycle while listening for the internal cooling fan (distinct from the hood/vent fan). If you do not hear it running, or it is very noisy, there may be a fan issue.
• If F8 appears quickly, stop and disconnect power.

Internal inspection (over-the-range models):

• Remove the unit from the wall if necessary to access the rear and top covers (this often requires two people).
• Locate the internal cooling fan motor near the magnetron and high-voltage components.
• Check for obstructions, broken fan blades, or seized bearings.

Corrective action:

• Replace a failed or noisy internal cooling fan motor.
• If the fan tests good but does not receive power when it should, the control board fan relay may be defective and the board may need replacement.

Warning: Due to high-voltage risks, fan and internal airflow repairs are best handled by a qualified technician.