Hi: I have a Thermador 4 burner gas stove top with, I believe, automatic piezo ignitors on each burner. The ignitors all fire symultanously when starting but once one of the burners light they are supposed to stop firing but they don't. I have cleaned all the ignitors using various cleaning agents with a toothbrush and dried them throughly but to no avail. All four continue to spark away driving one crazy from all the clicking noise. The unit worked properly when new. What could be causing this problem?