I don't do these, but it's at one of our customer's. Had gas pressure but not volume.
I found the gas regulator on the back of the flat top coated with gooo. The vent plug was restricted. I cleaned it and the flat top worked for a couple of hours.
The customer will not call a food equipment company, but did call the dealer that sold the top to him. The dealer stated it didn't need a regulator and just take it off. He said they are self regulated. Is that true? Our plumber installed it, and said the regulator came with the top. I don't really trust that the top doesn't need a regulator.