My Viking 24 inch range is operates on propane. When I turn on the oven, it lights fine and comes to temperature fine. After the preheat - the flame and light go off. It won't relight to maintain temperature. Is this a problem with the thermostat or the burner(s)? We're in remote Alaska and need to repair this ourselves. It worked fine for the first year. Thanks for any help and suggestions on part numbers.