Diagnosis
The burner is getting too much air or not enough air for complete combustion. Primary suspect: clogged burner ports or a misaligned burner cap.
How to Fix It
Clean and realign.
1. Remove the grate, burner cap, and burner base.
2. Inspect the small holes around the side of the burner base. Use a stiff brush (a toothbrush works) and a needle to clear any food debris or spider webs from the ports.
3. Ensure the burner base's slot aligns perfectly with the electrode and the gas valve orifice. It must sit flat.
4. Ensure the cap is centered and level.
If That Didn't Work
The gas regulator on the range might be faulty, but this is rare. It would affect all burners, not just one.
Heads Up
A yellow flame produces carbon monoxide. Always run your hood vent when this happens and fix it immediately. Do not use the burner until it burns blue.