Oven trips the circuit breaker or RCD when turned on or when heating

Safety first: Do not repeatedly reset a tripping breaker. Disconnect power and have the circuit inspected. Risk of shock and fire is significant.

• Visual inspection: With power off, remove the rear cover and inspect all wiring for burns, melted insulation, or contact with sharp metal edges.
• Test elements to ground: Disconnect each heating element and measure resistance between each terminal and the metal chassis. Any low resistance indicates a short; replace that element.
• Check mains filter: Inspect the interference suppression filter (often near the terminal block) for cracks or burns. Replace if damaged.
• Dry moisture: If the oven was recently cleaned with large amounts of water or steam, allow it to dry thoroughly before retesting.

Recommendation: Because this involves protective devices and earth leakage, a qualified electrician or appliance technician should perform final testing.