Oven trips the circuit breaker or RCD as soon as it is turned on or when heating starts.

Safety first: Do not repeatedly reset a breaker that trips immediately; this indicates a potentially dangerous fault.

• Visual inspection: With power off, remove rear and top covers. Look for burnt wires, melted insulation, or signs of arcing around elements and wiring harnesses.
• Element insulation test (basic): Disconnect each Toshiba heating element and try powering the oven briefly. If the breaker no longer trips, the disconnected element is likely shorted and should be replaced.
• Check EMI filter: Inspect the mains filter board for cracks, burn marks, or exploded capacitors. Replace if damaged.
• Dry out moisture: If the oven was recently cleaned with excessive water or exposed to leaks, allow it to dry for 24–48 hours with doors open before retesting.

For full insulation resistance testing, a qualified technician with a megohmmeter is recommended.