After eight years in the house without any problems now the oven circuit breaker keeps tripping as soon as the oven is above about 250 C. I turn off everything else that might be on this circuit and still the problem exists. Help!

Can be caused by a defective heating element, a loose connection in the oven or at the breaker, or a defective breaker.

The circuit and oven needs troubleshooting done to locate the actual problem.

You may want to have a look at the oven first, then check the circuit wiring and breaker if no problem is found in the oven.

If it's a standard range and only the oven trips the breaker, you should check the range fuses (they should blow before the breaker). If the oven fuse has not been tampered with, it must be a faulty breaker in the panel.

I don't see the range as being the problem- unless a range fuse is bypassed and you use only one element.

I would first look at the breaker. Replace the breaker with a new one. A breaker is cheaper and easier to replace than a range!