Oven trips the circuit breaker or RCD when heating is started.

Safety first: Do not repeatedly reset a tripping breaker. Disconnect power and keep it off until the fault is found.

• Visual inspection: Remove rear and top panels to inspect wiring to all heating elements. Look for melted insulation or wires touching the metal chassis.
• Element insulation test: With power off and wires disconnected, use a megohmmeter (insulation tester) between each element terminal and earth. Low resistance indicates leakage; replace the element.
• Dry moisture: If the oven was recently cleaned with excessive water or steam, allow it to dry thoroughly for 24–48 hours with the door open before retesting.
• Filter module: Inspect the mains interference filter for burn marks or cracking. Replace if damaged.

Because this involves safety earth and insulation testing, professional diagnosis is recommended.