We just bought a house with a thermador cooktop model GGNCV30 with the downdraft venting system. The right front burner doesn't spark, at least most of the time - gas is fine and works with a match. Other burners spark fine, but also spark when you try to start the problem burner. We think it just needs to be cleaned - repair guy (not a thermador person)said he couldn't get inside, and that the whole thing should be replaced. We don't think the cooktop should be replaced if all it needs is to be cleaned out. Help please.