One of the burners, the large center one, one my Bosch gas cooktop won't light itself. I can easily light it with a lighter, so there's definitely gas flowing. It clicks, and I can see a spark from the igniter, but it never actually lights. This seems like a very simple mechanism, so I'm not clear on what could be going wrong. What should I do to troubleshoot this? The rest of the burners light fine.