Microwave shows E3 and will not heat, fan may run briefly then stop.

Safety first: Unplug the Commercial Chef microwave. Do not operate with covers removed. High voltage components can be lethal.

Ventilation and usage checks:

• Verify that the microwave has at least several inches of clearance on all sides and that the rear vents are not blocked by walls or objects.
• Remove any items stored on top that may block top vents.
• Try a short 30-second test after the unit has cooled for 30–60 minutes. If E3 returns immediately, proceed to internal checks.

Internal checks (for trained or experienced DIYers only):

• Remove the outer cabinet and locate the magnetron thermal cutout (TCO) mounted on or near the magnetron body.
• With the unit unplugged, disconnect the TCO leads and test for continuity. A good TCO should read near 0 Ω. An open reading indicates it has tripped or failed.
• If tripped, inspect the cooling fan motor and air ducting for obstructions (dust, plastic wrap, etc.). Spin the fan by hand; it should move freely.
• Replace a failed TCO with the exact temperature rating specified for Commercial Chef models. Do not bypass or substitute with a different rating.

Important: Repeated TCO failures often indicate a failing magnetron or chronic airflow problems. If the new TCO trips again, stop using the microwave and have a professional evaluate the magnetron and high-voltage system.