I had the same issue with my Camp Chef stove on my brew pot. I check the company's website and they said that it has gotten dirty. I had left it on my decl and it had built up a bunch stuff ranging from rust to insects and what not.
Their suggestion was to blast with compressed air FROM the vent and blow out the dirt and debris. If you don't have a compressor they suggest using a strong blast iof water, only make sure it is dry before lighting it again.
Got tired of waiting for our savior to save the economy, so I jumped into all grain, What the hell!!!