Microwave stops heating mid-cycle and displays E4; unit may feel very hot externally.

Safety first: Unplug the microwave and allow it to cool for at least 30 minutes before inspection. Do not bypass any thermostats or thermal cutouts; they are critical safety devices.

Steps to address E4:

• 1. Check ventilation: Ensure the microwave has proper clearance on all sides. Remove any items blocking the intake or exhaust vents. Clean dust and grease from vents with a soft brush and vacuum.
• 2. Listen for cooling fan operation: During normal use, you should hear the internal cooling fan running whenever the magnetron is active. If the fan is silent or intermittent, the fan motor may be failing.
• 3. Access thermostats: Remove the outer cabinet. Locate the thermal cutouts/thermostats on the magnetron body and on the top or side of the cavity (Tristar models typically use disc-type thermostats with two terminals).
• 4. Test continuity: With the unit unplugged and cooled, disconnect one wire from each thermostat and test for continuity with a multimeter. A normally closed thermostat should show continuity at room temperature. If open, it has tripped or failed and must be replaced.
• 5. Inspect cooling fan: Check that the fan blades spin freely and are not obstructed by debris. Test the fan motor for continuity and replace if open or seized.
• 6. Replace faulty parts: Replace any open thermal cutouts with exact Tristar-specified parts. Reassemble, restore power, and test. If E4 recurs, discontinue use and consult a professional, as the magnetron may be overheating due to internal failure.