Microwave shows E3 and stops heating; fan and light may still operate.

Critical safety warning: Unplug the microwave. The high-voltage system (transformer, capacitor, diode, magnetron) can store lethal charge. Do not attempt high-voltage testing or capacitor discharge unless you are trained and equipped.

External checks:

• Ventilation: Confirm that all vents are clear and that the unit has adequate space around it. Remove any items blocking side or rear vents.
• Usage pattern: If E3 appears after long cooking cycles, the unit may be overheating due to poor ventilation or a failing cooling fan.

Internal airflow checks (qualified persons only):

• Remove the outer cabinet to access internal components.
• Locate the cooling fan motor and ensure the fan blades spin freely and are not obstructed by debris.
• Inspect the magnetron thermostat / thermal cutout mounted on or near the magnetron. Look for signs of overheating or discoloration.
• With power disconnected, test the thermostat for continuity using a multimeter. An open thermostat that does not reset when cool must be replaced.

If components are faulty:

• Replace a failed cooling fan motor if it does not run during cooking.
• Replace an open magnetron thermostat / thermal cutout with the exact Hamilton Beach-specified part.
• If the magnetron is overheating repeatedly or shows signs of arcing/burn marks, the magnetron may be failing and should be replaced by a professional.

Do not bypass safety thermostats; doing so can cause fire or severe damage.