How do I fix an Hygena Classic 910G Gas Oven?

Problem has developed with the oven today in that when the oven is turned, ignition successfully lights gas but continues to spark continuously until the oven is turned off. There does not appear to be a problem with the system inside the oven compartment. Is this an expensive repair in which case we will purchase another built in oven. The current oven appears to be about 7 years old.