Microwave stops heating shortly after start and displays E02 or will not start heating at all with E02 on the display.

Safety warning: Unplug the microwave. High-voltage components inside can be lethal. Do not work near the capacitor or magnetron unless you are competent and understand discharge procedures.

• Check ventilation: Ensure the microwave has adequate clearance on sides, top, and rear as specified in the Bush manual. Remove any obstructions from vents. Clean dust and grease from intake and exhaust grills.
• Inspect cooling fan: Remove the outer cover. Locate the cooling fan (usually near the magnetron). Spin the fan blades by hand; they should move freely. If seized, noisy, or not running during operation (observe briefly with cover loosely in place, taking care to avoid live parts), the fan motor may be faulty.
• Test thermal cut-outs: Locate the thermal fuses/thermostats on the magnetron and on the cavity/top of the oven. With power unplugged and wires removed, test each with a multimeter for continuity. Any open (infinite resistance) device that should be normally closed must be replaced.
• Check for grease buildup: Excess grease on the waveguide cover or cavity ceiling can cause localized overheating. Clean with a mild detergent and soft cloth; do not use abrasive pads.
• Reset vs replace: Some thermostats are auto-resetting; if they have tripped due to blocked vents, clearing the blockage may restore operation. One-shot thermal fuses must be replaced with the exact rating specified for Bush models.

If E02 returns after replacing faulty TCOs and ensuring proper ventilation, the magnetron or control board may be misreading temperature and should be diagnosed by a professional.