How to mend Oven ignition which starts up again after Full Flame attained?

Rangemaster Classic 90 gas FSD ( Natural Gas).
Wife dropped baked patato on gas burner area. Now can spark up oven burner but after 20 secs or so of full flame the sparker starts up again and continues - both oven and hobs! very irritating so have to stop using gas oven and use electric fan oven. What could be wrong and how can it be corrected?